I have an itinerary SNA-JFK-POP, returning POP-JFK-LAX in early January. However, SNA-JFK is in one ticket (flagship business), JFK-POP round trip on JetBlue ticket (economy), JFK-LAX is in the third ticket (flagship business).

Outbound JFK layover is from 5:50AM to 8:07AM. I am not too concerned about this layover since it is going from domestic to international.

Return JFK layover is from 4:36PM to 7:30PM for 2 hour and 54 minutes. Since this one involves clearing US customer at JFK, I am curious if this connection time is too risky? I have global entry and pre-check and I wont have any checked luggage, but I am concerned about time spending in line at US custom and leaving airside to landside at T5 and then go through security again. Can these be done within 3 hours? Once I am in landside, should I go through security check at T5 or T8? Is airtrain better than taking the new JetBlue-AA shuttle from T5 to T8?

Would winter time be problematic for this type of connection at JFK?

If I am lucky enough to arrive at Terminal 5 gate before 5:30PM, is flagship business ticket eligible for same-day airport change at the gate if there is an open business class seat for the 6PM flight to LAX?