is there a shutoff timer on a new ipad

Sort of. It won't shut it down completely, but it will put your iPad in slumber, which uses very minimal battery power. Go to Settings and on the right side of the main settings screen you'll Auto-Lock. Touch it and you can set your iPad to Auto-Lock from 2, 5 10, 15 or Never. Choose the time that best suits your needs.

Biggest power draw is the screen, that's why there is the setting to have the screen go to sleep after a certain period of inactivity.

Unless you plan on going into a coma, I wouldn't worry about power loss during music playback.

A fully charged iPad playing audio files back with the screen off should last at least 48 hours(I am making a Guess).

Considering it will act as a wifi hotspot for 25 hours with the screen off, I think 48 hours is a little on the low side.

I am using the iPhone SleepTimer on my iPad

http://i1224.photobucket.com/albums/ee374/Diavonex/32d46f31.jpg

That'd be plain crazy, you can fall asleep listening to music on your iPad and the screen will go off to save battery.