If you booked this through Orbitz, does that mean your original rescheduled flight had an AC code number but was operated by United? Certainly the SFO-SAN flight must be an United flight.

Figure out what combination of United/AC flights that you could take after 4 PM, that will get you from YEG-SAN, and push for that with the supervisor. It's possible you could be rerouted or accept an additional connection.