It's a great way to see Tikal if you are limited on time. I spent about 4.5 hours in Tikal, and I think that's enough time to see pretty much everything there with the tour guide (Aquilino), who is very friendly and knowledgeable about Mayan history and culture.
Here's how it went (FYI): I got picked up at a hotel in Zone 9 in Guatemala City at 4:30am; checked-in with Aeromar/G Airways to Flores (Note: you can bring liquid onboard, there's no liquid limitation on domestic flights in Guatemala...and it's important because once you pass security, there's only a waiting hall with bathrooms and nothing else). Flight was on-time, 50 min to Flores. Once at Flores at around 7:30, I was greeted by someone with a sign with my name on it. I hanged out at the cafeteria next door until 8am when we (the tour group) departed for Tikal. It took about an hour and a half to get to Tikal, and we made couple stops: first to check out the model of the Tikal site with bathrooms and shops for about 15-20 min; second was a quick stop to take picture of the lake. We arrived at Tikal at about 9:30. On the way walking to the different temple, we ordered lunch (a choice of beef, chicken, port, veggie, comes with rice and veggie). The lunch is served after we were done with the tour at Tikal, and the restaurant is within the site. I think we got to the restaurant at about 2:30 and after that we left the site. Since we got a bit of time, for those who were flying back to GUA, the tour guy arranged a quick stop at Flores Island for 50 min (4:30-5:20ish) before we were dropped off at about 5:30 at the airport for the 7:20pm flight back to GUA. At the Flores Airport, there's a cafeteria where I had a quick dinner before flight. Other options are available across the street slightly to the east of the airport where there's a shopping center with Pizza Hut, McDonald's and Taco Bell. Again, after security at the airport, there's waiting hall with bathrooms only. Flight back was on-time and got picked up again at GUA back to the hotel. Everything went smoothly with no issues. It's a long day but it is perfect if you are short in-time and really want to visit Tikal (which is the best Mayan site I've visited so far, and I've been to Tulum, Coba, Chichen Itza, Altun Ha, and Iximche)