Both of these places are geared to touring. Most people simply book a tour and go to either one. They make it very difficult to do anything else. Xcaret would be my choice, for the day, especially if you take in the supper show. You can also make reservations to have dinner while watching the show if you would like to do that. I have never noticed any public transportation. The closest would be in Playa del Carmen. Then you would still have to taxi in and out. This would be quite troublesome. You could rent a car at your hotel and go there for the day. I did this once. The trip there in the day was fine. I thought it would be a problem at night, but there are so many busses to follow out it turned out OK. The main highway Mex. 307 is 4 or 6 lanes in places and well lite. The other option is to book your own 8 passenger van at the Grand Mayan. They usually hang out with the taxi guys. Make a deal to drive you out and pick you up at a certain time and in a certain place. Money talks in Mexico. Anything is possible. I think everything is over by 9 pm. It is very busy when the place closes, so even stay together with your friends as you leave.