Shoot to be back at your resort an hour before your magical express bus time which in turn is about 3 hours before your flight. Be at the bus platform -- kids, carry-ons, etc. all ready -- 15 minutes before your scheduled bus.
In your case, with the 1:05 flight, if you leave your resort, your ballpark plan to be back should be for about 9:05 which for most practical purposes means you should not leave your resort that morning.
If you are using resort checked baggage check in (RAC), you must complete it 3 hours in advance of your flight but be aware that being in the RAC line does not count as punctual for your DME bus. If you cut it closer and T-15 arrives with you still in line, then leave the line and schlep the baggage to the bus platform.
Go to the right platform! * Particularly if you arrived by some means other than DME, you should observe DME picking up other sad, departing, guests on a prior day which will also familiarize yourself with the platform location.
While at the bus platform, inquire and verify that every bus pulling in is not yours before sitting back down and waiting some more.
If you are denied boarding your DME bus, within five minutes after it leaves, go in and ask the resort concierge to hire a taxi for you. Among other things, to make more people aware of the problem on that bus run and to put more irons in the fire to solve this problem; even if the bus driver radioed for another bus. Unlike buses leaving the parks at closing time or DME buses going to Disney, if a DME bus back to the airport does not take everyone in line and reserved on it, that is Disney's problem that needs instant solution.
* (OT) Once in an earlier lifetime I got off the metro and went to catch the shuttle bus back to the airport and waited and waited. All of a sudden I remembered that I didn't go down the stairway that I went up when I got off the shuttle earlier in the day to get on the metro. I was at the wrong platform! I raced across the metro station to the other platform and fortunately caught a shuttle in time to make my plane. I'll comment on "get in the right towncar" and "pick up the right gas pump hose" in future threads relevant to those subjects.