The descriptions of most tours are vague and ambiguous, so I thought I'd detail what happened on our tour. It may differ from day to day and guide to guide, but this was what happened on the May 10 tour.
First, it was virtually impossible to contact the tour company. They didn't respond to two emails, and my phone calls before we left home just rang unanswered. I wanted to be sure they had contact info for us that worked in Mexico (since my phone didn't). Our airport shuttle driver was finally able to get through to them on his phone. They sent a text confirming our pickup time and location at 9:30pm the night before the tour.
We were picked up from the northern part of the Cancun hotel zone by the 19 person van at 6:45am, and headed South to Playa Carmen. Along the way we picked up 7 more guests for a total of 9 on the tour. The tour company rents out space for a table in a gift shop in Playa Carmen, and you exchange your voucher and $40 for park fees there in exchange for a wristband. You can use the toilets there and buy a hat, sunscreen, water, etc. if you forgot something.
At 8:30 we left for Chichen Itza, and were given a sack meal with a sandwich, fruit drink box, and fruit or cookie to tide us over until lunch. We arrived in the park at 11:15 and got a 1:15 tour of the central area (El Castillo, ball court, etc.), followed by 45 minutes on our own. We used the free time to see the observatory, nunnery, etc. in the South.
At 1:15 we left Chichen Itza and at 2:45 arrived at Ek Ballam. We had a 45 minute tour, including time to climb to the top for those who wanted to. We arrived at the Cenote/restaurant around 3:40 and had a buffet lunch. The food was fine (though tourist bland), and you could go back as many times as you wanted. Just be aware that all drinks are extra (water is $2, soda is $3 and beer is $4) and no outside drinks are allowed. Afterwards we had access to the cenote until they closed at 5:00.
We left at 5:00, dropped off the other guests at 7:15, and we were dropped off last at around 8:00pm.
I picked this tour because it visited two archeological sites and had a minimum of wasted tourist trap time (gift shop, restaurant, "cultural" event). I had hoped that the advertised 6am start time implied an early park arrival, but no such luck - that time was spent driving south to Playa Carmen and picking up other guests. I was happy with the tour overall, though I didn't realize that it was based out of Playa Carmen. If you are staying in Cancun you could save a couple hours of pointless driving by selecting a company based there.