As a West Coast listener, this move really confuses me. The only plausible reason I can think of is Jim is targeting the drive time audience on the East Coast. His listeners on the West Coast, where most of his fanbase is, will probably drop off due to the time change. 12-3 is quite different than 9-noon. I think most of us in California are much more likely to be listening to the radio in the earlier time slot. We're also much more likely to be driving in our car.
If someone disagrees, please leave a response. Because the move has confused quite a few of my friends as well.