Who does this regularly? I try to do the loop at least twice a week. I live on the UWS so I can do a loop or two after work and it usually isn't too crowded. I usually do the loop in around 20 minutes (only been riding for a short amount of time) and it's amazing to see the serious riders in the city just fly by me.
On the weekends the park is too crowded so I've been on 9W in Jersey, and last weekend I took Metro North to Greenwich and did a 20 mile loop up to Bedford, which was awesome. I also want to go up to Bear Mountain one weekend.