Just got back after 5 days and using the bus. The schedule is the same between parks as posted. TRAFFIC is an unknown that can vary your times. I tracked routes on my phone, and they often don't take the most direct highway route, so are susceptible to possible delays. Like others, 20 min. seems about average. Our longest trip was from AK to EPCOT at night, which I think actually topped out around 35 minutes. But very professional, and always left on time.
***
So, I just happened to think up a mnemonic device on the trip that actually allowed me to remember the schedule without referring to paper, which was convenient when sitting in dark on a ride and trying to think up the next options! I'll post it here, in case it might help others
First, you do have to know the basic layouts of the Parks geographically, or it probably won't help.
If you are familiar, think of a square, and where each park would be positioned on each corner of that square if you had to assign them each to a single corner. It would be:
[Magic Kingdom] [EPCOT]
[Animal King] [H. Studios]
Now, think of a clock. When the hands are straight up-and-down, they're at "0" and "30" past the hour. These are the N/S vertical routes on the square, and the only 30 minute combo that "fits" the same direction on the map as a clock (i.e. 10/40 and 20/50 aren't diagonal or horizontal on a clock).
Next, think of trucker movies from the 70's and CB Radios. Remember the phrase "10-40 good buddy"?. When you think of truckers (and their historic usage of CBs), you think of them driving cross-country, especially coast-to-coast. That's generally considered east-to-west and vice versa (horizontal). Also, CBs are old, and the oldest parks are MK and EPCOT, so another way to remember 10/40 is horizontal.
Finally, you're left with 20/50, a diagonal. There's only one remaining path, but if you think of 20/50 being the most "complex" sounding of the 3, and diagonals are more "complex" than basic horizontal or vertical lines, then you can remember it's parks that you'd make diagonal lines in the hypothetical square are the 20/50 times. Or forget "complex" and remember that in a square the diagonal line is a *longer* line than the straight lines that connect the corners so it's numerical length will be a LARGER number than the other lines, and 20/50 is the LARGEST combined number of the 3 as well.
Hence, as has been posted back in Post 1135, you can see how this (0/30 = vertical, 10/40 = horizontal, 20/50 = diagonal) all fits the schedule:
MK - EP 10/40
MK - DHS 20/50
MK - AK 0/30
EP - MK 10/40
EP - DHS 0/30
EP - AK 20/50
DHS - MK 20/50
DHS EP 0/30
DHS - AK 10/40
AK - MK 0/30
AK - EP 20/50
AK - DHS 10/40
Yes, mnemonic devices are pretty stupid but if you can remember at least 2 of the 3 triggers I mentioned (with the last being the default) maybe it can work for you to some extent as well!