It's very quiet, I used to take this flight on a monthly basis, I fine tuned it so I would arrive at JFK at around 7.50-8.00 for the 9am departure (having OLCI'd), there is never a queue for J/F check-in or for security screening. It is VERY civilised and VERY easy!
This week all departures are an hour earlier because UK clocks go forward a week before US clocks... But you will be fine if you arrive at JFK at around 7 - 7.15am.