Just happened on my last flight 9:30a departure PBI-JFK, we pushed 10 minutes early.
We were at the gate eating breakfast at Chili's didn't hear any boarding announcement. At 30 minutes before departure (15 before the gate deadline) they were all ready making PA customer pages by passenger name that the plane was immediately departing.
Not an full flight, I would say 80% full.
Landed 31R in front of T5, heavy breaking and right into the gate. Once of my fastest trips. Flight was then going to DAB.