diff --git a/crates/bevy_core/src/lib.rs b/crates/bevy_core/src/lib.rs
index 10daf75022e312..3e61aeeb72fba6 100644
--- a/crates/bevy_core/src/lib.rs
+++ b/crates/bevy_core/src/lib.rs
@@ -15,7 +15,7 @@ pub use time::*;
 pub mod prelude {
     #[doc(hidden)]
     pub use crate::{
-        DefaultTaskPoolOptions, EntityLabels, FixedTimestep, Labels, Name, Time, Timer
+        DefaultTaskPoolOptions, EntityLabels, FixedTimestep, Labels, Name, Time, Timer,
     };
 }
 
diff --git a/crates/bevy_core/src/time/fixed_timestep.rs b/crates/bevy_core/src/time/fixed_timestep.rs
index 48237e638131bd..009172f0b8d6ca 100644
--- a/crates/bevy_core/src/time/fixed_timestep.rs
+++ b/crates/bevy_core/src/time/fixed_timestep.rs
@@ -1,10 +1,6 @@
-use bevy_ecs::{
-    schedule::ShouldRun,
-    system::{Res, ResMut}
-};
-use bevy_utils::Duration;
+use bevy_ecs::{schedule::ShouldRun, system::ResMut};
 
-use crate::Time;
+use bevy_utils::Duration;
 
 #[derive(Debug, Clone)]
 pub struct TimeAccumulator {
@@ -14,19 +10,16 @@ pub struct TimeAccumulator {
 
 impl Default for TimeAccumulator {
     fn default() -> Self {
-        Self { 
-            time: Duration::from_secs(0), 
-            steps: 0
+        Self {
+            time: Duration::from_secs(0),
+            steps: 0,
         }
     }
 }
 
 impl TimeAccumulator {
     pub fn new(time: Duration, steps: usize) -> Self {
-        Self { 
-            time, 
-            steps
-        }
+        Self { time, steps }
     }
 
     /// The number of accrued steps.
@@ -43,14 +36,14 @@ impl TimeAccumulator {
 
     /// The amount of time accrued toward the next step as [`f32`] % of timestep.
     pub fn overstep_percentage(&self, timestep: Duration) -> f32 {
-        self.time.div_duration_f32(timestep)
+        self.time.as_secs_f32() / timestep.as_secs_f32()
     }
 
     /// The amount of time accrued toward the next step as [`f64`] % of timestep.
     pub fn overstep_percentage_f64(&self, timestep: Duration) -> f64 {
-        self.time.div_duration_f64(timestep)
+        self.time.as_secs_f64() / timestep.as_secs_f64()
     }
-    
+
     /// Add to the stored time, then convert into as many steps as possible.
     pub fn add_time(&mut self, time: Duration, timestep: Duration) {
         self.time += time;
@@ -74,22 +67,19 @@ impl TimeAccumulator {
     }
 
     pub fn reset(&mut self) {
-        self.time = 0.0;
+        self.time = Duration::from_secs(0);
         self.steps = 0;
     }
 }
 
-
 pub struct FixedTimestep;
 
 impl FixedTimestep {
-    pub fn step (
-        mut accumulator: ResMut<TimeAccumulator>
-    ) -> ShouldRun {
-        if let Some(_) = accumulator.sub_step() {
+    pub fn step(mut accumulator: ResMut<TimeAccumulator>) -> ShouldRun {
+        if accumulator.sub_step().is_some() {
             ShouldRun::YesAndCheckAgain
         } else {
             ShouldRun::No
         }
     }
-}
\ No newline at end of file
+}
diff --git a/crates/bevy_core/src/time/time.rs b/crates/bevy_core/src/time/time.rs
index c6c7b710a41dda..d2186df03a3fd0 100644
--- a/crates/bevy_core/src/time/time.rs
+++ b/crates/bevy_core/src/time/time.rs
@@ -1,8 +1,7 @@
 use bevy_ecs::system::ResMut;
 use bevy_utils::{Duration, Instant};
 
-use bevy_ecs::system::ResMut;
-use bevy_utils::{Duration, Instant};
+use crate::TimeAccumulator;
 
 /// Tracks time elapsed since the previous update and total frame time since the app was started.
 #[derive(Debug, Clone)]
@@ -94,8 +93,8 @@ impl Time {
     pub fn fixed_delta_seconds_f64(&self) -> f64 {
         self.fixed_delta_seconds_f64
     }
-    
-    /// Changes fixed delta. Users are strongly cautioned against modifying 
+
+    /// Changes fixed delta. Users are strongly cautioned against modifying
     /// the step rate this way, except during startup.
     /// Prefer [`Time::set_speed_multiplier`] to ensure consistent simulation behavior.
     pub fn set_steps_per_second(&mut self, steps: f32) {
@@ -121,6 +120,7 @@ impl Time {
     /// Set rate app time advances relative to true clock time.
     #[inline]
     pub fn set_speed_multiplier(&mut self, speed_multiplier: f32) {
+        assert!(speed_multiplier > 0.0);
         self.speed_multiplier = speed_multiplier;
     }
 
@@ -172,12 +172,12 @@ impl Time {
     }
 }
 
-pub(crate) fn time_system(
-    mut time: ResMut<Time>,
-    mut accumulator: ResMut<TimeAccumulator>
-) {
+pub(crate) fn time_system(mut time: ResMut<Time>, mut accumulator: ResMut<TimeAccumulator>) {
     time.update();
-    accumulator.add_time(time.delta().mul_f64(time.speed_multiplier_f64()), time.fixed_delta());
+    accumulator.add_time(
+        time.delta().mul_f64(time.speed_multiplier_f64()),
+        time.fixed_delta(),
+    );
 }
 
 #[cfg(test)]
@@ -204,7 +204,10 @@ mod tests {
         // Fixed delta is fixed.
         assert_eq!(time.fixed_delta(), Duration::from_secs_f32(1.0 / 64.0));
         assert_eq!(time.fixed_delta_seconds(), time.fixed_delta().as_secs_f32());
-        assert_eq!(time.fixed_delta_seconds_f64(), time.fixed_delta().as_secs_f64());
+        assert_eq!(
+            time.fixed_delta_seconds_f64(),
+            time.fixed_delta().as_secs_f64()
+        );
 
         // Sanity check.
         assert_eq!(time.last_update(), None);
@@ -226,7 +229,10 @@ mod tests {
         // Fixed delta is still fixed.
         assert_eq!(time.fixed_delta(), Duration::from_secs_f32(1.0 / 64.0));
         assert_eq!(time.fixed_delta_seconds(), time.fixed_delta().as_secs_f32());
-        assert_eq!(time.fixed_delta_seconds_f64(), time.fixed_delta().as_secs_f64());
+        assert_eq!(
+            time.fixed_delta_seconds_f64(),
+            time.fixed_delta().as_secs_f64()
+        );
 
         // Sanity check.
         assert_eq!(time.last_update(), Some(first_update_instant));
@@ -234,7 +240,10 @@ mod tests {
 
         // App advances 1:1 to with real time.
         assert_eq!(time.speed_multiplier(), 1.0);
-        assert_eq!(time.time_since_startup(), first_update_instant - start_instant);
+        assert_eq!(
+            time.time_since_startup(),
+            first_update_instant - start_instant
+        );
 
         // Update `time` again and check results
         let second_update_instant = Instant::now();
@@ -249,7 +258,10 @@ mod tests {
         // Fixed delta is STILL fixed.
         assert_eq!(time.fixed_delta(), Duration::from_secs_f32(1.0 / 64.0));
         assert_eq!(time.fixed_delta_seconds(), time.fixed_delta().as_secs_f32());
-        assert_eq!(time.fixed_delta_seconds_f64(), time.fixed_delta().as_secs_f64());
+        assert_eq!(
+            time.fixed_delta_seconds_f64(),
+            time.fixed_delta().as_secs_f64()
+        );
 
         // Sanity check.
         assert_eq!(time.last_update(), Some(second_update_instant));
@@ -257,11 +269,14 @@ mod tests {
 
         // App advances 1:1 to with real time.
         assert_eq!(time.speed_multiplier(), 1.0);
-        assert_eq!(time.time_since_startup(), second_update_instant - start_instant);
+        assert_eq!(
+            time.time_since_startup(),
+            second_update_instant - start_instant
+        );
 
         // Make app time advance at 2x the rate of real world time.
         time.set_speed_multiplier(2.0);
-        
+
         // Update `time` again 1 second later.
         let third_update_instant = second_update_instant + Duration::from_secs(1);
 
@@ -274,7 +289,10 @@ mod tests {
         // Fixed delta is still fixed.
         assert_eq!(time.fixed_delta(), Duration::from_secs_f32(1.0 / 64.0));
         assert_eq!(time.fixed_delta_seconds(), time.fixed_delta().as_secs_f32());
-        assert_eq!(time.fixed_delta_seconds_f64(), time.fixed_delta().as_secs_f64());
+        assert_eq!(
+            time.fixed_delta_seconds_f64(),
+            time.fixed_delta().as_secs_f64()
+        );
 
         // Sanity check.
         assert_eq!(time.last_update(), Some(third_update_instant));
@@ -282,6 +300,9 @@ mod tests {
 
         // App is advancing at 2x speed, so app time should have advanced by 2 seconds.
         assert_eq!(time.speed_multiplier(), 2.0);
-        assert_eq!(time.time_since_startup(), second_update_instant - start_instant + Duration::from_secs(2));
+        assert_eq!(
+            time.time_since_startup(),
+            second_update_instant - start_instant + Duration::from_secs(2)
+        );
     }
 }
diff --git a/examples/3d/spawner.rs b/examples/3d/spawner.rs
index 9f54fceb4c504d..fecf9d22aad52f 100644
--- a/examples/3d/spawner.rs
+++ b/examples/3d/spawner.rs
@@ -30,8 +30,7 @@ fn move_cubes(
     for (mut transform, material_handle) in query.iter_mut() {
         let material = materials.get_mut(material_handle).unwrap();
         transform.translation += Vec3::new(1.0, 0.0, 0.0) * time.delta_seconds();
-        material.base_color =
-            Color::BLUE * Vec3::splat((3.0 * time.seconds_since_startup()).sin());
+        material.base_color = Color::BLUE * Vec3::splat((3.0 * time.seconds_since_startup()).sin());
     }
 }
 
diff --git a/examples/ecs/fixed_timestep.rs b/examples/ecs/fixed_timestep.rs
index 136ba2d856283a..3fe7fe40d342ca 100644
--- a/examples/ecs/fixed_timestep.rs
+++ b/examples/ecs/fixed_timestep.rs
@@ -23,28 +23,31 @@ fn main() {
         .run();
 }
 
-fn set_fixed_timestep(
-    mut time: ResMut<Time>,
-) {
-    time.set_steps_per_second(10);
+fn set_fixed_timestep(mut time: ResMut<Time>) {
+    time.set_steps_per_second(10.0);
 }
 
-fn frame_update(
-    mut last_time: Local<f32>,
-    time: Res<Time>,
-) {
-    info!("time since last frame_update: {}", time.seconds_since_startup() - *last_time);
+fn frame_update(mut last_time: Local<f32>, time: Res<Time>) {
+    info!(
+        "time since last frame_update: {}",
+        time.seconds_since_startup() - *last_time
+    );
     *last_time = time.seconds_since_startup();
 }
 
-fn fixed_update(
-    mut last_time: Local<f32>,
-    time: Res<Time>,
-    accumulator: Res<TimeAccumulator>,
-) {
-    info!("time since last fixed_update: {}\n", time.seconds_since_startup() - *last_time);
+fn fixed_update(mut last_time: Local<f32>, time: Res<Time>, accumulator: Res<TimeAccumulator>) {
+    info!(
+        "time since last fixed_update: {}\n",
+        time.seconds_since_startup() - *last_time
+    );
     info!("fixed timestep: {}\n", time.fixed_delta_seconds());
-    info!("time accrued toward fixed_update: {}\n", accumulator.time());
-    info!("time accrued toward fixed_update (% of time.fixed_delta): {}", accumulator.overstep_percentage());
+    info!(
+        "time accrued toward next fixed_update: {}\n",
+        accumulator.overstep()
+    );
+    info!(
+        "time accrued toward next fixed_update (% of time.fixed_delta): {}",
+        accumulator.overstep_percentage(time.fixed_delta())
+    );
     *last_time = time.seconds_since_startup();
 }
diff --git a/examples/ecs/iter_combinations.rs b/examples/ecs/iter_combinations.rs
index 2d137e0b7722af..67ef108067df44 100644
--- a/examples/ecs/iter_combinations.rs
+++ b/examples/ecs/iter_combinations.rs
@@ -6,24 +6,22 @@ struct FixedUpdateStage;
 
 fn main() {
     App::new()
-    .insert_resource(Msaa { samples: 4 })
-    .add_plugins(DefaultPlugins)
-    .add_startup_system(set_fixed_timestep)
-    .add_startup_system(generate_bodies)
-    .add_stage_after(
-        CoreStage::Update,
-        FixedUpdateStage,
-        SystemStage::parallel()
-        .with_run_criteria(FixedTimestep::step)
-        .with_system(interact_bodies)
-        .with_system(integrate),
-    )
-    .run();
+        .insert_resource(Msaa { samples: 4 })
+        .add_plugins(DefaultPlugins)
+        .add_startup_system(set_fixed_timestep)
+        .add_startup_system(generate_bodies)
+        .add_stage_after(
+            CoreStage::Update,
+            FixedUpdateStage,
+            SystemStage::parallel()
+                .with_run_criteria(FixedTimestep::step)
+                .with_system(interact_bodies)
+                .with_system(integrate),
+        )
+        .run();
 }
 
-fn set_fixed_timestep(
-    mut time: ResMut<Time>,
-) {
+fn set_fixed_timestep(mut time: ResMut<Time>) {
     time.set_steps_per_second(100);
 }
 
@@ -149,10 +147,7 @@ fn interact_bodies(mut query: Query<(&Mass, &GlobalTransform, &mut Acceleration)
     }
 }
 
-fn integrate(
-    time: Res<Time>,
-    mut query: Query<(&mut Acceleration, &mut Transform, &mut LastPos)>
-) {
+fn integrate(time: Res<Time>, mut query: Query<(&mut Acceleration, &mut Transform, &mut LastPos)>) {
     let dt_sq = time.fixed_delta_seconds() * time.fixed_delta_seconds();
     for (mut acceleration, mut transform, mut last_pos) in query.iter_mut() {
         // verlet integration
diff --git a/examples/game/alien_cake_addict.rs b/examples/game/alien_cake_addict.rs
index 3d3ea3cf593fa0..8ece2b1d1b44b6 100644
--- a/examples/game/alien_cake_addict.rs
+++ b/examples/game/alien_cake_addict.rs
@@ -71,10 +71,8 @@ struct Game {
     camera_is_focus: Vec3,
 }
 
-fn set_fixed_timestep(
-    mut time: ResMut<Time>,
-) {
-    time.set_steps_per_second(1 / 5.0);
+fn set_fixed_timestep(mut time: ResMut<Time>) {
+    time.set_steps_per_second(0.2);
 }
 
 const BOARD_SIZE_I: usize = 14;
diff --git a/examples/game/breakout.rs b/examples/game/breakout.rs
index ebfc7de2dcc5b3..d6261bc3199cf1 100644
--- a/examples/game/breakout.rs
+++ b/examples/game/breakout.rs
@@ -209,7 +209,7 @@ fn paddle_movement_system(
     translation.x = translation.x.min(380.0).max(-380.0);
 }
 
-fn ball_movement_system(mut ball_query: Query<(&Ball, &mut Transform)>) {
+fn ball_movement_system(time: Res<Time>, mut ball_query: Query<(&Ball, &mut Transform)>) {
     let (ball, mut transform) = ball_query.single_mut();
     transform.translation += ball.velocity * time.fixed_delta_seconds();
 }