2 minutes 20 seconds is 2.33 minutes, so 2.33 x 100=233 minutes or a little under 4 hours, which isn't too bad of screen on time, but you can get better depending on your setup.
ive never actually had anything help my battery life significantly like this free app i found today. try it out, im still amazed that I'm still at 80%. it seems that screen display had always been my issue. check it out though pretty cool.
krisION is correct, that can help alot also. ive actually as of lately been turning off my data and or wifi with my screen turning off. still get my calls and text while saving a buttload of battery.