Its been a few years now since Ive been to Tulum (also from Cozumel). Our ship did not let us off in Playa del Carmen, so there was the time of taking the 40 minute ferry over to the main land. Then a 60-90 minute bus ride to the ruins. I don't recall exactly how long we stayed at the site, but it was very nice. Right on the coast with a beautiful view. Yes, HOT! Bring a swim suit, theres a swimming area. I believe we arrived back later in the day, had some time for some shopping but as mentioned above.... that heat plus the walking and riding seems to drain you. We did (maybe foolishly) grab a bite to eat with some fellow pax. I remember it was just getting dark as we headed back to the ship.