I believe that many of the shops in Old San Juan may be closed or closing druing those times. If there is a festival going on, you may see street vendors and hear music near where the ship docks. (Actually, since the port was renovated and more ships dock here, you may see the street vendors all the time. If you are really lucky, you may see a fireworks display. There's also plenty of nightlife in the Condado and Isla Verde areas where hotels and casinos offer gaming and cabaret shows. You'll need to take a cab to those. A walk around Old San Juan streets in the early evening can still be interesting. Be prepared for plenty of traffic, steepish hills, narrow sidewalks and the occasional young person who just needs a few more coins for bus fare home. However, it will be cooler than during the day, and those wonderful spanish lanterns look so romatinc glowing on the street corners. And though most of the shops close, in the late afternoon you can almost always find the Walgreens open and doing a brisk trade--a good place to stock up on sunscreen, film, and sodas for the room if you need 'em.
