Well CP loop is about 6.1 miles. Assuming 6 miles, 20 mph average would take you 18 minutes. So that or less is good time. Only problem is the traffic there. You would have to be riding *really early* in the morning (5:30am) to have a clear road. You might see some others training there that you could hook up with. Its been a while since I've ridden there that early. Also, be careful in that you could get a red light ticket. I have seen others get that and a fixed gear rider getting a ticket for not having a brake in CP. I don't know where you got the times above. Are they for a partial loop?

Edit: I saw the chart here: https://nycc.org/rides I have commuted with 16 mph in the morning give or take. So the chart says that I would be comfortable with 1:30 (hour and a half) to 1:38. I originally thought that those were minutes and not hours.