Remember that the AKL has its own bus service (does not share with other resorts). Therefore, eventhough it is farther away from all the parks, it doesn't take long at all to get there since it doesn't make any other stops (even at resort, there is only one stop).
Figure:
MK- 15 minutes
Epcot- 10 minutes
MGM- 10 minutes
AK- <5 minutes
I would say 45 minutes will give you PLENTY of time, even if you just missed a bus. When we were there in December 2003 (very slow time) busses came every 10 minutes or so. We thought the AKL had the best bus service out of all the resorts we have stayed at.