The 12 Hours of Bradbury is a 12-hour mountain bike endurance race held each fall at Bradbury Mountain State Park in Pownal Maine. I've entered the event twice. Both times as part of a 4 man team. The average race lap takes about an hour. With a 4 man team, each rider takes turns 'racing' a lap. That allows plenty of time to recover (and socialize!) in between laps.
That's the way us older guys roll!