ESPN greed to get it all. This is a game that should have been on ABC or ESPN 2, but now that Mickey's evil cousin has almost all the bowl games, they want to run them all back to back on the mother station.
Granted it is a west coast game, but it is a bowl game that is affiliated with the Big 12 and Big 10, there is no good reason this game should be starting that late. How many west coast viewers are going to be interested in that game. The Kraft Bowl in San Francisco is on at 5pm on ESPN 2, that is the game that should have the late start. I bet the ratings end up about the same for both games.
IMO this shows how espn doesn't really care about the ratings of a lot of these games, since they already have everyone paying for them in the base programming packages.