In my experience, aren't all meals served roughly at the points during the flight, regardless of the flight length or departure time? .

On flights with two full meals, the first is served ~1 hour after takeoff, and the 2nd around ~1.5 hours before landing. If there's a snack service between the meals, it almost always falls at the midpoint of the flight.

I've personally never been on a flight that's deviated from this schedule.