The Rolex 24 hour race at the Daytona International Speedway was the premier event of the Grand-Am Series prior to the merger with American Le Mans Series which has resulted in the Tudor United SportsCar Series. TUSC continues to use Rolex 24 as their opening round, and is the longest endurance race in the US on a professional level. Daytona 24 was my first major endurance race in the US and I have completed this race for the past two years.
Registering for the event is pretty straight forward. It helps to be an SCCA member if you are from the US as the Central Florida SCCA region organizes the volunteers. However there are plenty of foreign marshals volunteering the event as well, so your credentials may get you in just fine.