Respuesta :

Shy614
. . . Well, I don't know what clocks you are referring to. 
But if they played for 50 minutes, and stopped playing at 11:20 PM, rewind 50 minutes before that, and they will have started playing at 10:30 PM.

But if they stopped playing at 11:20 AM,  rewind 50 minutes before that, and they will have started playing at 10:30 AM.