They were running into at least the early afternoon last week. I watched the second Cavalcade in Frontierland, did a few nearby things, and then walked to Main Street. I have photos of the Dapper Dans taken around 1:00 with vehicles going by in the background.
That said, OP, the vehicles don't seem to have a set daily schedule and the best plan is to ride them early if you want to be sure to ride them.