In 3 of the last 4 flights I've taken, boarding was the limiting factor. We left the gate within 5 minutes after the last person boarded, and were airborne shortly after without having to wait on the tarmac. On one of those flights, the plane didn't finish boarding until 10-15 minutes after it was scheduled to take off.
Curiously, the one exception was a United red-eye back from SF to Boston. And I think they may've been using this boarding method - the gate attendants said that the boarding groups were window seats first, then middle, then aisle. There certainly was no rhyme or reason to seating within boarding groups, and there were about 12 boarding groups.
But when did you start boarding? When did the planes arrive? They usually make you start boarding about 20 minutes before they are allowed to take off, so people sit in the plane the minimum amount of time.
Planes usually arrived about 40-45 minutes, sometimes up to an hour before we started boarding.
In 2 of the 3 flights, that might've been the case. But that other one, we were actually late, so I don't think they delayed boarding so we wouldn't have to wait. Actually, we started boarding about 15-20 minutes after we were scheduled to start boarding.
Cleaning seems like the real bottleneck, but assuming they can't get the flight attendants to work any faster, any time saved on boarding shortens the deplane/clean/board cycle.
Curiously, the one exception was a United red-eye back from SF to Boston. And I think they may've been using this boarding method - the gate attendants said that the boarding groups were window seats first, then middle, then aisle. There certainly was no rhyme or reason to seating within boarding groups, and there were about 12 boarding groups.