Here's a few spots I've enjoyed at night:
Good snorkeling in the evening off sun dollar, big stuff comes in to feed, Alberto's restaurant often has eagle rays at dusk, hotel barracuta has plenty of octopus and squid, the cenote outflow by the lighthouse in town has plenty of little stuff at dusk.
Depends how many night's you have and your skill in the water.... perhaps a generous tip to one of the dive shop workers would have a guide for you if you are hesitant on your own to handle the risks.
Regards,
Cameron