While we have cleared up what time zone applies, the questions raised in the original post (OP) (arrival date -- landing time versus CBP) and in Posts # 2 to 4 (departure date -- airline schedule versus actual take-off) have not been definitively answered.

It seems pretty clear that arrival is based on CBP clearance time.

For departure, airlines routinely use the scheduled departure time for crediting a mileage earning date. So if a flight departs early or late, the original boarding pass remains valid. CBP has no record of when each aircraft's wheels left the runway, and therefore presumably would rely upon a boarding pass / airline records.

However, if a flight is canceled and rescheduled to a new date (Eastern Time), it would be hard to argue one had still "departed" the United States on the original date. In such circumstances, if the 90-day period had been exceeded, one would be well advised to seek and obtain a grant of Satisfactory Departure from USCIS or CBP to maintain ESTA, VWP, and visa eligibility.