One of my friends put an app on the Play store. Brilliant idea. Simple program. Free. It's called Tymey.
When you put your phone on vibrate or silent mode with your volume buttons, a timer option will pop up. It allows you to set how long you want your phone to stay on silent or vibrate. It will turn the ringer back on automatically after the allotted time.
It's great for when you are about to go into a movie, or a meeting etc. I'm constantly missing calls because I forget to turn my ringer back on after meetings. Give it a try:
https://play.google.com/store/apps/d...ne.tymey&hl=en