Bank vault timers were invented in 1874 to discourage potential robbers from kidnapping bank personnel and forcing them to open the vault. The timer can be set for a predetermined amount of time; once the time is up, a bolt moves into place, allowing the door to open. Most timers have more than one clock to set, in case one fails. Otherwise the vault door might have to be forced off.
Determine the next time the vault will need to be accessed.
Determine what time the bank vault will be closed.
Add the hours from the time the vault will be closed until it will need to be accessed again. That number will be the hours that should be set on the bank vault timer.
Many bank vault timers list only whole numbers. If your calculation includes a fraction of an hour, round down in order to avoid complications when it comes time to open the bank vault.