Just to echo the above, I live on the UES and 6am ex-LGA is my preferred way to leave town. I normally get a car at 5:00-5:10 and arrive at the gate just as my group boards. The FDR/Triboro/GCP are all wide open that time of morning. If you leave at 3 you'll be there at 3:15-20 with nothing to do for 2 hours.