Rudd is an app for Pebble that gives you a new perception of time. Start by setting an interval anywhere from 1 minute to 1 hour, and then you're good to go.
A set vibration interval for your watch has a surprising number of applications. For example, when you're doing a workout and want to exert yourself for a certain amount of time without having to check your watch, a simple vibration lets you know when you're done with your current rep. Set the watch for 30 to 60 minutes to give yourself a reminder to take a study break when your hard at work. And you can play a mind trick on yourself by setting a 5 minute timer to see how fast time flies by when you're having fun at a party versus when you're bored waiting in a line. The possible applications are endless.