I would say this is an aspect of Flighty's algorithms and assumptions. The gate opened at 12:37, C62, so almost exactly an hour to departure, and entirely normal. Yes if the flight was only half full and departing A gates then I imagine the agents would be a bit later, and it's also the case that if the flight was full agents would want to get pre-boarding out of the way as soon as possible, given that the aircraft had been at the gate 3 hours before departure as the inbound from SFO. But ultimately anyone at the gate at 13:20, the usual cut-off, would have been boarded, and probably for a few minutes after too.