diff --git a/documentation/new-notes/PR-744.md b/documentation/new-notes/PR-744.md
new file mode 100644
index 000000000..27dcbfadd
--- /dev/null
+++ b/documentation/new-notes/PR-744.md
@@ -0,0 +1,12 @@
+### Avoid early expiration of timers on non-RTOS
+
+Previously, the epicsTimer code rounded down user requested delays by subtracting one half
+of the sleep "quantum".
+On RTEMS and vxWorks, this allowed periodic timers which expired on every tick.
+However, this also resulted in
+timers expiring slightly [earlier than requested](https://github.com/epics-base/epics-base/issues/106).
+
+With [PR 744](https://github.com/epics-base/epics-base/pull/744)
+rounding is only done for RTEMS and vxWorks, which still have tick timers.
+
+This effects several facilities which use epicsTimer, including record delays.  eg. `calcout.ODLY` becomes more [accurate](https://github.com/epics-base/epics-base/issues/106#issuecomment-1260232765).
diff --git a/modules/libcom/src/timer/timer.cpp b/modules/libcom/src/timer/timer.cpp
index 679ca27ef..f7da1c476 100644
--- a/modules/libcom/src/timer/timer.cpp
+++ b/modules/libcom/src/timer/timer.cpp
@@ -65,7 +65,11 @@ void timer::start ( epicsTimerNotify & notify, const epicsTime & expire )
 void timer::privateStart ( epicsTimerNotify & notify, const epicsTime & expire )
 {
     this->pNotify = & notify;
-    this->exp = expire - ( this->queue.notify.quantum () / 2.0 );
+    this->exp = expire
+#ifdef TIMER_QUANTUM_BIAS
+            - ( this->queue.notify.quantum () / 2.0 )
+#endif
+            ;
 
     bool reschedualNeeded = false;
     if ( this->curState == stateActive ) {
diff --git a/modules/libcom/src/timer/timerPrivate.h b/modules/libcom/src/timer/timerPrivate.h
index eea26808f..f221ee54c 100644
--- a/modules/libcom/src/timer/timerPrivate.h
+++ b/modules/libcom/src/timer/timerPrivate.h
@@ -35,6 +35,16 @@
 #   define debugPrintf(ARGSINPAREN)
 #endif
 
+/* For historical reasons, round down expiration time on vxWorks and RTEMS.
+ * Targets with a fixed timer period.
+ * This biasing down by half a period allows timers which expire on every tick.
+ * Otherwise, the fastest timer is 2x the tick period.
+ * This results in timers expiring one period earlier than requested.
+ */
+#if defined(vxWorks) || defined(__rtems__)
+#  define TIMER_QUANTUM_BIAS 1
+#endif
+
 template < class T > class epicsGuard;
 
 class timer : public epicsTimer, public tsDLNode < timer > {
diff --git a/modules/libcom/test/Makefile b/modules/libcom/test/Makefile
index a19a9bac0..8c3da6928 100644
--- a/modules/libcom/test/Makefile
+++ b/modules/libcom/test/Makefile
@@ -10,6 +10,9 @@
 TOP = ../../..
 include $(TOP)/configure/CONFIG
 
+# allow tests to peek at private headers
+USR_CPPFLAGS += -I$(TOP)/modules/libcom/src
+
 PROD_LIBS += Com
 PROD_SYS_LIBS_WIN32 += ws2_32 advapi32 user32
 PROD_SYS_LIBS_solaris += socket nsl