you must allow an hour from your hotel to the hertz office that morning to pick up your car and drive back to the hotel to pick up the family
(i just paid $55 for overnight parking at the Essex House- so its no savings picking up the car the night before)
having the limo show up on time saves you that hassle
and if you have never driven in manhattan- there are odd rules (like no turns onto some avenues) - and "boxes" -crosshatched intersections- that you do not want to be stuck in when the light changes- get a ticket and your driving schedule is shot
you may hear it referred to as "limo" or "town car" or "black car" but its usually a lincoln town car
for a family of 4 with luggage you may want to splurge on a stretch to ensure you have enough room