Another better option is "SBSchedule". This app allows you to set up different profile for different times of day. They can be manually set or set to come on at a certain time of day or night. You can set Phone, Wifi, 3G, Data, screen brightness, ringer volume, and any other app that has a SBToggle compatibility. For example I have set up several profiles. I'm retired so they apply to my situation.
Home Mode - WiFi - on, 3g, data, E - off: Brightness about 50%, ringer volume about 50%, ....
Out and About - 3g, data, E, Firewall - on: WiFi - off: Brightness about 70%, ringer volume 100%
Night Mode - WiFi, 3g, Data, E - off; brightness about 25%, ringer volume about 40%, Starts at 12am
Day Mode - starts at 7am, same as home mode.
Works great! Really cuts battery consumption down to a reasonably low level.