diff --git a/libraries/AP_Logger/LogStructure.h b/libraries/AP_Logger/LogStructure.h
index 432ce26376bb5..b2a858a16f303 100644
--- a/libraries/AP_Logger/LogStructure.h
+++ b/libraries/AP_Logger/LogStructure.h
@@ -556,6 +556,7 @@ struct PACKED log_Performance {
     uint32_t i2c_count;
     uint32_t i2c_isr_count;
     uint32_t extra_loop_us;
+    uint64_t rtc;
 };
 
 struct PACKED log_SRTL {
@@ -895,14 +896,15 @@ struct PACKED log_VER {
 // @Field: MaxT: Maximum loop time
 // @Field: Mem: Free memory available
 // @Field: Load: System processor load
-// @Field: IntE: Internal error mask; which internal errors have been detected
+// @Field: InE: Internal error mask; which internal errors have been detected
 // @FieldBitmaskEnum: IntE: AP_InternalError::error_t
 // @Field: ErrL: Internal error line number; last line number on which a internal error was detected
-// @Field: ErrC: Internal error count; how many internal errors have been detected
+// @Field: ErC: Internal error count; how many internal errors have been detected
 // @Field: SPIC: Number of SPI transactions processed
 // @Field: I2CC: Number of i2c transactions processed
 // @Field: I2CI: Number of i2c interrupts serviced
 // @Field: Ex: number of microseconds being added to each loop to address scheduler overruns
+// @Field: R: RTC time, time since Unix epoch
 
 // @LoggerMessage: POWR
 // @Description: System power information
@@ -1211,7 +1213,7 @@ LOG_STRUCTURE_FROM_MOUNT \
     LOG_STRUCTURE_FROM_BEACON                                       \
     LOG_STRUCTURE_FROM_PROXIMITY                                    \
     { LOG_PERFORMANCE_MSG, sizeof(log_Performance),                     \
-      "PM",  "QHHHIIHHIIIIII", "TimeUS,LR,NLon,NL,MaxT,Mem,Load,ErrL,IntE,ErrC,SPIC,I2CC,I2CI,Ex", "sz---b%------s", "F----0A------F" }, \
+      "PM",  "QHHHIIHHIIIIIIQ", "TimeUS,LR,NLon,NL,MaxT,Mem,Load,ErrL,InE,ErC,SPIC,I2CC,I2CI,Ex,R", "sz---b%------ss", "F----0A------FF" }, \
     { LOG_SRTL_MSG, sizeof(log_SRTL), \
       "SRTL", "QBHHBfff", "TimeUS,Active,NumPts,MaxPts,Action,N,E,D", "s----mmm", "F----000" }, \
 LOG_STRUCTURE_FROM_AVOIDANCE \
diff --git a/libraries/AP_RTC/AP_RTC.cpp b/libraries/AP_RTC/AP_RTC.cpp
index a57c3242852fd..7a2f6e7efd44b 100644
--- a/libraries/AP_RTC/AP_RTC.cpp
+++ b/libraries/AP_RTC/AP_RTC.cpp
@@ -9,6 +9,12 @@
 #include <GCS_MAVLink/GCS.h>
 #include <AP_Common/time.h>
 
+#define DEBUG_RTC_SHIFT 0
+
+#if DEBUG_RTC_SHIFT
+#include <AP_Logger/AP_Logger.h>
+#endif
+
 extern const AP_HAL::HAL& hal;
 
 AP_RTC::AP_RTC()
@@ -47,9 +53,19 @@ void AP_RTC::set_utc_usec(uint64_t time_utc_usec, source_type type)
 {
     const uint64_t oldest_acceptable_date_us = 1640995200ULL*1000*1000; // 2022-01-01 0:00
 
-    if (type >= rtc_source_type) {
-        // e.g. system-time message when we've been set by the GPS
-        return;
+    // only allow time to be moved forward from the same sourcetype
+    // while the vehicle is disarmed:
+    if (hal.util->get_soft_armed()) {
+        if (type >= rtc_source_type) {
+            // e.g. system-time message when we've been set by the GPS
+            return;
+        }
+    } else {
+        // vehicle is disarmed; accept (e.g.) GPS time source updates
+        if (type > rtc_source_type) {
+            // e.g. system-time message when we've been set by the GPS
+            return;
+        }
     }
 
     // check it's from an allowed sources:
@@ -70,6 +86,11 @@ void AP_RTC::set_utc_usec(uint64_t time_utc_usec, source_type type)
     }
     WITH_SEMAPHORE(rsem);
 
+#if DEBUG_RTC_SHIFT
+    uint64_t old_utc = 0;
+    UNUSED_RESULT(get_utc_usec(old_utc));
+#endif
+
     rtc_shift = tmp;
 
     // update hardware clock:
@@ -83,6 +104,32 @@ void AP_RTC::set_utc_usec(uint64_t time_utc_usec, source_type type)
     // update signing timestamp
     GCS_MAVLINK::update_signing_timestamp(time_utc_usec);
 #endif
+
+#if DEBUG_RTC_SHIFT
+    uint64_t new_utc = 0;
+    UNUSED_RESULT(get_utc_usec(new_utc));
+    if (old_utc != new_utc) {
+        if (AP::logger().should_log(0xFFFF)){
+            // log to AP_Logger
+            // @LoggerMessage: RTC
+            // @Description: Information about RTC clock resets
+            // @Field: TimeUS: Time since system startup
+            // @Field: old: old time
+            // @Field: new: new time
+            // @Field: in: new argument time
+            AP::logger().WriteStreaming(
+                "RTC",
+                "TimeUS,old_utc,new_utc",
+                "sss",
+                "FFF",
+                "QQQ",
+                AP_HAL::micros64(),
+                old_utc,
+                new_utc
+                );
+        }
+    }
+#endif
 }
 
 bool AP_RTC::get_utc_usec(uint64_t &usec) const
diff --git a/libraries/AP_Scheduler/AP_Scheduler.cpp b/libraries/AP_Scheduler/AP_Scheduler.cpp
index 7085e05541d22..0c3ae78f87e2b 100644
--- a/libraries/AP_Scheduler/AP_Scheduler.cpp
+++ b/libraries/AP_Scheduler/AP_Scheduler.cpp
@@ -447,6 +447,11 @@ void AP_Scheduler::update_logging()
 // Write a performance monitoring packet
 void AP_Scheduler::Log_Write_Performance()
 {
+    uint64_t rtc = 0;
+#if AP_RTC_ENABLED
+    UNUSED_RESULT(AP::rtc().get_utc_usec(rtc));
+#endif
+
     const AP_HAL::Util::PersistentData &pd = hal.util->persistent_data;
     struct log_Performance pkt = {
         LOG_PACKET_HEADER_INIT(LOG_PERFORMANCE_MSG),
@@ -464,6 +469,7 @@ void AP_Scheduler::Log_Write_Performance()
         i2c_count        : pd.i2c_count,
         i2c_isr_count    : pd.i2c_isr_count,
         extra_loop_us    : extra_loop_us,
+        rtc              : rtc,
     };
     AP::logger().WriteCriticalBlock(&pkt, sizeof(pkt));
 }