Its hard to give a MAXIMUM taxi time.. I would say its possible to take 2 hours in some extreme condition, 3 is unthinkable.. but then I suppose anything is possible if the highway is suddenly closed, and you happen to be already on the road..

1) at 3am it should be less than an hour.. might even be 45 minutes
2) at 9am it is more likely to be a 70 to 90 minute ride depending on traffic

The guy at the Adelphi can get a cab for you in advance if you like.. but in most cases.. the cabs are parked just outside.. and he will even go get one for you..