Ride to the top without breaking at the ranger station to get a feel for the ride.

Other than that do what Ericm says above. You can go to the mountain, and get through the private road to the old south entrance. Then do your 20 minute intervals from there, it will improve your time. Keep in mind that the challenge is all about 11 miles of climbing and is mostly sustained output (there is a short break at the pay gate past rock city).

As for drinking there may be someone at the ranger station to hand you a cup of water during the actual event. :-)