I've had neighbors who are pilots (and 1 was a backup pilot who was always on call when someone couldn't show up).

They've explained that your hours count ONLY when the plane has closed the door and backed away from the gate. Then you are officially being paid for your time.

This explains the horror stories of "stuck on the runway". It's usually issues with weather/equipment/airport, etc. and it's not in the crew's best interest to just stay at the gate until the issue is resolved. If you're at the gate, the crew is not being paid.