There are times when your Mac may not want to go to sleep, and it’s probably because of something that is running in the background preventing the OS from wanting to go to into the standby mode. If you’ve come across a similar situation the free PleaseSleep app might be exactly what you need.
This is designed to counteract apps which are able to prevent your Mac from going to sleep. If you have an app that is preventing your computer from going to sleep this will throw down the gauntlet and put your Mac to sleep anyway at the duration specified in the Energy Saver preferences.
Where might this be useful? One situation I can think of is when watching a video. Some of the video apps on your computer might try to prevent your machine from going to sleep while watching the movie. With this app you can still force the machine to go to sleep even if the movie is running, which will effectively make it act like a sleep timer for your machine.
You can also dig around the settings to do things like specify whether this should take precedence all of the time, or only when certain apps are running. You can also exclude certain apps so that if they are running PleaseSleep won’t take any special action.
PleaseSleep Homepage (Mac only; Freeware)