If you view the track log, the pilot changed direction at around 3.36am after take off at 3.12am (both times EDT as reported on FlightAware). So that's 24 minutes into the flight, not 90 (the entire flight SFO-SFO was 1hr20). It was cruising at 30,000 feet though when it started the diversion.
https://flightaware.com/live/flight/...605Z/KSFO/KSFO
https://flightaware.com/live/flight/.../KSFO/tracklog