5 hours?
Cab to Old San Juan, go to La Taberna Lúpulo, drink craft beers for for 2 hours, then go to El Batey, drink crap beer (or good rum) for another hour, then cab back to the airport.
Or cab to Condado, barhop, and get some food for 3 or so hours.
I also have a layover coming up from 2:30 am to 7:30 am on a Tuesday night/Wednesday morning. Which casinos in Condado are open, and which bars/restaurants?