Actually, it did not work properly, as it seems that the timer was never reset. I ended up adding an extra bool:
if sound_16.status == STARTED and mouse1.isPressedIn(polygon) and stopwatchStart == True:
pass
elif sound_16.status == STARTED and stopwatchStart == True:
sound_16.stop()
t1 = sw.getTime()
elif mouse1.isPressedIn(polygon):
sw.reset()
stopwatchStart = True
But thanks for the help, it is much appreciated!