Directors and Assistant Directors need to have an iron grip on time passing during the day. For years, I used a series of (silent) alarms to mark waypoints throughout the day. The only downside of this system has been having to adjust all of the alarms, manually, after receiving the callsheet each night. Time math takes me a minute (pun intended) at the best of times, but after a 14hr day, and while staring down the barrel of another pre-dawn call time, it gets a bit sketchy.