You can always get a late drink around Dam Square and have a walk around the canals. I agree that you should get a hotel at AMS and take the train in, but the train ride is only 10 or 12 minutes and they go constantly. If your flight lands at 740p you can be in the city by 900p and have a couple of hours lookaround. Just be sure you know the late-night outbound train schedule from Centraal.