I don't think there are any 'set' routes; one person's experience might be Caribbean Beach > Contemporary > Animal Kingdom; another's might be Contemporary > Wilderness Lodge > Polynesian; and yet another might be Boardwalk > Contemporary.
For your return trip, you are scheduled to get the DME bus three hours before your flight. There are a number of potential reasons for what some Guests consider an overly-long wait at the airport including but not limited to:
The bus may need to stop at one or two other resorts after yours;
There may be heavy traffic;
Long lines to check in (for Guests whose airlines don't participate) and/or at security.
For these and other possible reasons, is strongly inadvisable to pick your own return time. Just take the bus when you're scheduled.