We're planning to arrive at Tikal late in the evening and start exploring early the next morning.
We can either stay at Tikal that night also, or return to Flores and spend a night there (might be nice to see the lake etc).
Any opinions either way?
I guess the question is, how long do you need at Tikal? Is heading off at early-mid afternoon ok, or am I being silly trying to do it so quickly?
I think that after one night and a full day at Tikal, I think you would enjoy a night at Flores at a hotel located on the lake with a pool. Hotel Santana and Casona de la Isla meet this standard. At Hotel Santana all have balconies, but the best are those with a lake view on second floor. Reserve ahead.
Watching the sunset and its afterglow around the lake while eating and sipping a beer makes for an excellent beginning of any evening there. Either Mayan Sunset Cafe or Hotel Santana are good locations.
If you have the time, stay the extra night. You will find out when you get there that the place is huge and magical. Keep your options open.
Curious - how will you be arriving at Tikal late at night? Will you have a rental car? It's an unusual time to show up there. For most folks having the early morning hours and the rest of the day to explore would be enough, though you'll apparently miss the evening hours which I've enjoyed on my 2 visits. Where else are you planning to go on your trip? Is this primarily a Belize-with-Tikal visit or primarily a Guatemala trip? Do you prefer towns or would extra time in an amazing jungle setting with wildlife be preferable? Sorry for so many questions but my opinion would be based on them.

Another option is to stay in El Remate, which is about 20 minutes from the Tikal Park entrance. La Casa de Don David is cheap and nice place to stay and has a nice view of the lake. Remate is a VERY quiet town if tranquility is what you're after.

I am leaving for Tikal via economy bus from Antigua at 1pm and don't get in until after 10pm so that is how you arrive late there. The next bus is at 6:30PM and you get in 9 hours after that--so that is another way that you get there late. So to the person who said it was unusual to arrive there so late...no, it isn't!!
Sorry, dlkbc, any kind of public bus will take you to Santa Elena, not Tikal. The one exception is Linea Dorada, which can also drop you off at its office in Flores on Playa Sur. Getting to Tikal late would normally involve driving a rental car or hiring what would probably be a particularly expensive cab ride. The last public bus to Tikal leaves at 3 PM and I am not sure when the shuttles stop, but I doubt there will be any in even late afternoon.