JFK's T8 also handle several other inbound flights from abroad that go thru US Customs & Immigration so it's a matter of timing, GE is a definite plus and without checked luggage - so it's matter of quickly deplane & going thru, then out into landside & walk outside to get the free AirTrain, follow signs & direction to get to T5, should be doable but still too tight for my comfort - weather & landing/taxiway not delayed, etc. But, you can be home at your final destination late night instead of spending a hotel night near JFK.

B6 or JetBlue's T5 terminal is nicely done and is still very busy in the evening with both arrivals & departures, if your schedule is tight & no time to visit a lounge, good choice of food to quickly grab en route to your boarding gate. Shower is probably out of the question, IMO.

I am also guessing that this isn't one a single ticket but 2 different PNR so have a backup plan in case of a misconnect and B6 ticket are not cross-honored on other carriers. Late B6 departures are not unusual so if everything is running late and some are airport/weather-related, chances are that your B6 could be too.

Haven't heard of any weekend scheduled JFK AirTrain work or maintenance, in which case free shuttle bus services are provided - which they do but often resulted in extra travel time & delays with long lines. Keep that in mind & check the PANYNJ's Airport website for alerts/status by your weekend of travel.