I've used DME 3 or 4 times now, at different times of day, and on different days of the week. Although I have yet to arrive late at night, even after 5:00, so I can't say anything about those times.
I've had times of 60 mins to 90 mins so far. The 90 mins was on a Monday morning, about noon time. POP was the last of three stops (had always been stop number 1), and there were a lot of people with bags underneath the bus (they, for whatever reason, decided against using the baggage delivery) so it took a bit more time at each resort while the driver sorted through the appropriate luggage.
If you see a long line at the DME checkin counter, you will find that generally speaking they will have extra CM's working. They know when they are having a bunch of people arriving so they plan accordingly. Same with the buses.
It does really work out that the busier times will find more staff on duty, with more buses rolling.