Think music ends around midnight ...seems to be a trend towards longer headliner sets of 2 hours or so. Lower tier bands generally play just under an hour, starts to get over an hour the higher you get on the poster.
last year Jack Johnson was scheduled 10:45-12, Prince @ 10:45, and Roger Waters 8:30 - 11 with Justice playing the Sahara at 11. The Outdoor Stage was also dark when headliners played the Coachella Stage, but other smaller tents and the Sahara were going.
The actual set times and locations are usually released about a week or so before the show, so it will be awhile.