Originally Posted by
redreeper
I've flown IB MAD to JFK many times, I have Global Entry.
My fastest time through - wheels down to standing at the exit - 30 minutes. Longest, about one hour.
Getting on a flight leaving LGA at 3:45 - I would say you have no chance of doing that and I am sorry. The lengthy and unpredictable (as well as predictable) delays would start as soon as you left JFK.
I would give myself 4 hours between flights at very minimum. With no checked bags.
On my last IB flight back to JFK, 5 minutes after deplaning I was landside. Door opened about 30 second after attaching to jetway.
Personally, I could make it
IF arrival is on time and light traffic between airports; I have actually done it during an IRROP, arriving in LGA with hours of wait time. LGA/JFK/EWR are my home hubs.
All that said, OP, I would not do it. PERIOD.