A free app for Android, by Advanced Image Inc.

WiFi Timer is a useful utility that enables you to manage your WiFi connection on periodic basis. It enables you to manage the connection on the device itself and set it to either ON or OFF state. The app automatically takes care of the connection. You can set it ON for a particular time or for the period of time. 

When it is turned ON, it allows you to browse the internet and sync your emails, messages, etc. When it is turned OFF, the app will disconnect your device from the internet and will stop sending data. The app will automatically turn ON your WiFi connection when it is turned OFF and when it is turned ON again, it will sync all the data that was previously sent.