Set a timer for 12 hours to wake you up in 12 hours. This is a free and easy-to-use countdown timer that allows you to set the hour, minute, and second for the online countdown. Simply start the timer, and it will alert you when 12 hours have passed. Alternatively, you can set a specific date and time to count down to (or from) an event. Begin your 12 hours timer now for a quick and precise reminder.