There is no set amount of laps, you simply have to race for 2 hours. The final lap begins when the leader of the race crosses the start/finish line after 2 hours have passed, so the race can end on anywhere from lap 79 to lap 99. Some people like to park their car right in front of the finish line after they have gotten a big enough lead and wait for the 2 hour mark to pass, then gleefully cross the stripe to end the race. Others like to turn around and run the course backwards, engaging in such activities as pushing the cones around the track, bumping into the other cars, or holding up certain cars to let slower ones pass. Whatever floats your boat.