On my US Airways Shuttle flight BOS-LGA yesterday morning we pushed back 15 minutes before the scheduled departure time and were off the ground shortly after our quick taxi to runway 9. I've seen them close the aircraft door a few minutes early on flights before, and I have even seen them leaving a few minutes early before. This just seemed to be an extreme case, and with 40 shuttle trips to LGA last year, I have never experienced it. Does anyone know if there is any sort of FAA regulation regarding this out there? I did a Google search, but didn't uncover anything.