We did the Chichen Iza trip from Cancun with a group, rather from Progreso, so I have no idea the difference in the bus ride length.
Our bus ride seemed to last at least three weeks, and I got off without a book to read along the way. Our time at the ruins was maybe an hour and a half or so, it was terribly hot and there wasn't any shade. The ruins are incredibly impressive; I can't imagine what it took to accomplish what they did, but no way could I have climbed in that heat.
Then we went to have lunch and rode back. We did stop a few times for rest stops, and were accosted by hordes of people with outstretched hands.