Are you talking about going through TSA the night before? TSA at JFK especially is quite strict in regards to access, so you likely won't be allowed in the day before since your flight isn't until 8am the following morning.
Yeah, that was my plan. I knew they closed certain checkpoints, but I didn't realize they wouldn't admit for an overnight layover. How certain is this?
SleepingInAirports cites this as a possibility, but I've found a few DPs in the past year that it's not a concern in T8:
11pm - 6am,
midnight - 6am, and
mightnight - 7am.
I'm hopeful that the dedicated security for Flagship check-in will also be extra-lenient? This is pretty concerning for me though as I don't want to stay landside.