Here is the current schedule, December 1-16:
Magic Kingdom, Epcot:
8am-12:30pm, every 30 minutes
2:40pm
4:40pm till 7:40pm every 60 minutes
Hollywood Studios, Animal Kindom
8:15 to 12:15 every 30 minutes
3:25, 5:25, 6:25
Downtown Disney
3:25pm, 5pm, 7pm, 7pm
Returning:
Magic Kindom (open till 7pm, 8pm, 9pm, 12am, or 1am)
12:15, 2:20, 3pm, 5pm, 6pm, 7pm, then every 20 minutes till 11:40pm, plus 12:30am some nights
Epcot (open 9-9:30pm, fireworks at 9:30pm)
3:15, 5:15, 6:15, 7:15 then every 20 minutes till 9:55pm, then 10:30pm
Animal Kingdom (open 9-5, 9-6, or 9-7)
4pm, 5pm, 6pm, 7pm (on 3 nights only)
Hollywood Studios (open 9-5, 9-7, 9-8, 9-9, or 9-10)
4:15, 6:15, 7:15, 8:45, 9:50pm (on 3 nights only)
Downtown Disney
5:15, 7:10, 9:15, 12am
I'm assuming the bus goes Wyndham-MK-Epcot-MK-Wyndham, and it goes from Tower 6 to Tower 1 so if you are going from Tower 1 to Magic Kingdom it's a pretty fast journey, less so from Epcot to Tower 6. Also I guess the bus stops at Animal Kingdom then Hollywood Studios.
We have a car and we will not use the bus for AK or HS, but maybe we will try it for MK tomorrow to save $14.
Note you will need a taxi for Universal/SeaWorld, or to go shopping other than DTD.