I prefer to do the loop clockwise since I like to do trials on the granite when I'm fresh. The loop takes 2.5 to 4 hours depending on how much you want to goof off. The scenery is very cool. Be prepared for changing weather. Also have a plan ready in case someone gets hurt.
Spider lake is lower in elevation then loon.
I find the best way to do this trail is in parts. From Loon Lake campground take the fun pretty technical single track for maybe 8 miles without too much elevation change. Turn left and make the whole loop counterclockwise. Otherwise I recommend turning around at the top of the last hill before the Desolation Wilderness and head back to make a nice ride. The camp hosts can be very helpful.