Depending on the airline and aircraft, boarding will start 30 to 40 minutes prior to scheduled departure time so that turns a 8am departure to 7:20-7:30 boarding. I think flights close at 15 min prior to departure.

In theory, the first flight of the morning should be on time since it doesn't need to contend with any flights ahead of it, adding to the risk of missing the cut off.

I would also be concerned about the tsa and C&I staffing levels early in the morning. Will it be enough to handle the crush of the 100-200 people taking that first flight?