Update time_boss.py

start timing after appending the current instance to the global stack

time_boss/time_boss.py

@@ -57,8 +57,8 @@ def __init__(self, name: str):
         TimeBoss.all_timers[name] = self
 
     def __enter__(self):
-        self._start = perf_counter()
         TimeBoss.timer_stack.append(self)
+        self._start = perf_counter()        
 
     def __exit__(self, type, value, traceback):
         dt = perf_counter() - self._start