Some people will do that immediately after boarding, but you do of course run the risk of looking a bit silly if there is an emergency and you have to leave the aircraft in a hurry.

Remember also that at JFK there will only be a short walk to the gates so you don't have to take a long hike into account - I would think that 90 minutes would be ample for pre-flight dining. Personally I like to take my time so would aim to get to the airport a bit earlier and take my meal at a leisurely pace. Leaving time for digestion is a good idea. I also prefer to take a shower before boarding so try and build in some time for that and then I'm just about set for lights-out once we hit the top of climb.