diff --git a/src/wormhole/timing.py b/src/wormhole/timing.py
index e4f884d..1d7ace5 100644
--- a/src/wormhole/timing.py
+++ b/src/wormhole/timing.py
@@ -16,8 +16,8 @@ class Event:
     def detail(self, **details):
         self._details.update(details)
 
-    def finish(self, server_sent=None, **details):
-        self._stop = time.time()
+    def finish(self, when=None, server_sent=None, **details):
+        self._stop = time.time() if when is None else float(when)
         if server_sent:
             self.server_sent(server_sent)
         self.detail(**details)