I can definitely attest to being able to stay on the TTA for multiple rides. In fact, I was a part of a group of people that took it to the extreme level a few years back, and rode it non-stop for an entire day. It was a weekday in early December. Those in the group that went there right after park opening rode it for a total of 50 round-trips. (They could have done one more just before park closing, but they decided to stop at a nice, even number and get out of the park before the fireworks could finish).
In actuality, my friend and I were late getting there, and we took a couple breaks during the day. We originally thought we'd hop on for a couple trips, get off and do other things in the park, maybe stop in for another loop or two later in the day. But after the first couple loops, we had so much fun we decided to stay on. I think my total was around 38 loops, and my friend Brian had a couple more than I did.
Throughout the day, various people that knew what was going on stopped by for a ride. They knew what train number we were in (and after an hour or two, all the CMs knew the train number as well, so if someone asked, they'd know which one). Getting off for food or a restroom break and then meeting back up with Train 25 was easy, actually. Thanks to the TTA ride system, the loop was always the same length (except the single ride-stop we had during the day). So if you got off, you knew you had 10 1/2 minutes (or was it 11 1/2?) or a multiple of that length to get back to the platform to meet up with the train. At the end of the day, the CMs presented Magical Moments certificates to those who had been there all day.
It was actually a LOT more fun than I thought. We sort of developed our own "Rocky Horror Show"-type callbacks at the recorded spiels. One of which was singing "Great Big Beautiful Tomorrow" as we rode past Carousel of Progress. And coincidentally, there were a bunch of radio DJ tents set up outside CoP. You have to wonder what they thought of a train full of singing Guests cruising past them every ten minutes was all about...
-Rob