http://www.mgoblue.com/sports/brandon/spec-rel/120211aaa.html
A blog by Brandon detailing who picks the game times, etc.
Here is the most important quote: (My underlning)
Though our media partners have all the power in determining our kickoff times, the schools are allowed some autonomy when it comes to night games and which days of the week the game is played. The conference office and/or the network would have to ask us for permission if they felt a game would be better suited for its needs to be played at night or on another day.
If asked, the answer will be that Michigan regular-season home football games will always be played on Saturday and a night game will only be scheduled if it is a "special game" with significant fan interest. We are not going to schedule a home night game just to play a night game.
In addition, we have no plans to move Michigan State or Ohio State to a night game in Michigan Stadium.