Keep your eye on DL 1797, which is the ATL-SJC flight that will be the equipment for the return flight. It is scheduled to leave at 7:21 (eastern). This is three hours ahead of your friend's meeting's ending. If it is on time, then your friend should have no problem. If not, you have plenty of time to react.
Since it is the redeye, it will arrive in ATL at 6:10 which is a relatively slow time for ATL, so the flights will not be stacked up. The 7:30 flight is the first flight of the day to PHL so the equipment may overnight at the gate.
I honestly think at this time, your friend has a good chance of making the original itinerary.