For a reservation at that time, I would maybe allow a bit more than an hour, depending on which bus stop you are at for your route. I had a DTD reservation for dinner last year, and the bus that showed up at our stop was already mostly full, we were the last ones to cram onto it because we had to make our reservation. Assuming you get a bus that is not full, though, an hour would be plenty as it isn't too far walking from the bus to get to TREX. I don't think the commute is actually that bad, especially if you are using Disney transport, but DTD can get bad depending on the crowd level and where you are in relation to the construction (I remember it being difficult to maneuver through a "construction zone" where walls were up on a busy night, but it not being as bad when the crowds were lower or I was away from the construction).