I'm on an international flight at the end of march on a Friday that will be arriving at JFK AA terminal at 3:20pm. Will I have enough time to make a delta connection to Philly scheduled for 5:00 pm if I don't check luggage and am a US citizen?

Personally, I think you are cutting it extremely close and would much prefer a minimum of 2 hours. You could make your connection - assuming your inbound flight arrives at the gate on time and everything else goes smoothly but you have no room for error. Remember your connecting flight will begin boarding about 30 minutes prior to scheduled departure.

Passport Control lines for US Citizens usually move fairly quickly. We travel internationally often and are routinely through in anywhere from 5 to 15 minutes, however, you have to also factor in "walking time" from your arrival gate to Passport Control and that can add anywhere from 3 to 10 minutes depending on your arrival gate.

Customs is usually a breeze unless you are randomly singled out for a thorough inspection in which case there's no telling how long it will take.

You'll have to go through the TSA checkpoint once you get to the Delta terminal and that takes time - traditionally those lines move very slowly.

Of course, there's no guarantees your flight into JFK won't be arriving at the same as 6 jumbo jets. If that happens, all bets are off as both Passport Control and Customs can be a zoo!

So here's my best time estimates:

Deplane - 10 minutes
Walk to Passport Control - allow 10 minutes - be happy when it's less
Time waiting at Passport Control - 15 minutes
Customs - 5 minute (or less)
Walk to Sky Tram, wait for tram and ride to Delta Terminal - 20 minutes
TSA Screening - 20 minutes
WalK to Delta Gate - 10 minutes

Add all that up and you'll see realistically you've used up 75 to 80 minutes of your connection time - leaving you with some 20 to 25 minutes "extra" - not a lot but "doable" if all the stars align.

Hint, use Delta's on-line check-in feature to get your boarding pass before you leave on your international flight. That way you won't have to waste time standing on another line in the Delta terminal to get your boarding pass.

What are your options if you don't make it? That's what I'd consider first.

Personally for me it would be too tight. I hate to stress, so prefer 2-3 hrs on international flights (nothing specific about JFK or Delta, rather coming off an international flight anywhere).

That is pretty tight, as immigration clearance can be pretty variable. If you decide to try it, I would highly recommend checking in for the Delta flight online as you might miss the check-in cutoff if you try to do it at the airport.