diff --git a/klippy/reactor.py b/klippy/reactor.py
index 4c89b0fe..29ffe4f6 100644
--- a/klippy/reactor.py
+++ b/klippy/reactor.py
@@ -82,21 +82,18 @@ class SelectReactor:
         self._g_dispatch = None
         self._greenlets = []
     # Timers
-    def _note_time(self, timer_handler):
-        nexttime = timer_handler.waketime
-        if nexttime < self._next_timer:
-            self._next_timer = nexttime
-    def update_timer(self, timer_handler, nexttime):
-        timer_handler.waketime = nexttime
-        self._note_time(timer_handler)
-    def register_timer(self, callback, waketime = NEVER):
+    def update_timer(self, timer_handler, waketime):
+        timer_handler.waketime = waketime
+        self._next_timer = min(self._next_timer, waketime)
+    def register_timer(self, callback, waketime=NEVER):
         timer_handler = ReactorTimer(callback, waketime)
         timers = list(self._timers)
         timers.append(timer_handler)
         self._timers = timers
-        self._note_time(timer_handler)
+        self._next_timer = min(self._next_timer, waketime)
         return timer_handler
     def unregister_timer(self, timer_handler):
+        timer_handler.waketime = self.NEVER
         timers = list(self._timers)
         timers.pop(timers.index(timer_handler))
         self._timers = timers
@@ -106,18 +103,20 @@ class SelectReactor:
         self._next_timer = self.NEVER
         g_dispatch = self._g_dispatch
         for t in self._timers:
-            if eventtime >= t.waketime:
+            waketime = t.waketime
+            if eventtime >= waketime:
                 t.waketime = self.NEVER
-                t.waketime = t.callback(eventtime)
+                t.waketime = waketime = t.callback(eventtime)
                 if g_dispatch is not self._g_dispatch:
+                    self._next_timer = min(self._next_timer, waketime)
                     self._end_greenlet(g_dispatch)
                     return 0.
-            self._note_time(t)
+            self._next_timer = min(self._next_timer, waketime)
         if eventtime >= self._next_timer:
             return 0.
         return min(1., max(.001, self._next_timer - self.monotonic()))
     # Callbacks
-    def register_callback(self, callback, waketime = NOW):
+    def register_callback(self, callback, waketime=NOW):
         ReactorCallback(self, callback, waketime)
     def register_async_callback(self, callback):
         self._async_queue.put_nowait(callback)
@@ -158,22 +157,28 @@ class SelectReactor:
         if g is not self._g_dispatch:
             if self._g_dispatch is None:
                 return self._sys_pause(waketime)
+            # Switch to _check_timers (via g.timer.callback return)
             return self._g_dispatch.switch(waketime)
+        # Pausing the dispatch greenlet - prepare a new greenlet to do dispatch
         if self._greenlets:
             g_next = self._greenlets.pop()
         else:
             g_next = ReactorGreenlet(run=self._dispatch_loop)
         g_next.parent = g.parent
         g.timer = self.register_timer(g.switch, waketime)
-        return g_next.switch()
+        self._next_timer = self.NOW
+        # Switch to _dispatch_loop (via _end_greenlet or direct)
+        eventtime = g_next.switch()
+        # This greenlet activated from g.timer.callback (via _check_timers)
+        return eventtime
     def _end_greenlet(self, g_old):
         # Cache this greenlet for later use
         self._greenlets.append(g_old)
         self.unregister_timer(g_old.timer)
         g_old.timer = None
-        # Switch to existing dispatch
+        # Switch to _check_timers (via g_old.timer.callback return)
         self._g_dispatch.switch(self.NEVER)
-        # This greenlet was reactivated - prepare for main processing loop
+        # This greenlet reactivated from pause() - return to main dispatch loop
         self._g_dispatch = g_old
     # Mutexes
     def mutex(self, is_locked=False):