I think demo is a good choice. For a 3-5 hr ride, get to the top of ridge trail
(trailhead has a map) go down and go right onto Corral > left up Sulfur Springs
(watch for the left it comes up fast after the water bar jumps) back up to Ridge trail > Go right on Ridge to Sawpit > Right on Hilm (sp?) rd to climb back up to Sulfur Springs > Go up sulfur springs again > Right on Ridge trail to Braile > back out all the way up Hilm to the parking lot.
If you do this in under 3 hrs, most of us would kneel at your feet with food and treasure offerings
If you feel like you have not had enough, you can always climb Sulfur Spring a 3rd time and do Tractor. It's fast, smooth and fun.
Trailhead will get you a nice bike, but call ahead to make sure they have what you need availible.