It’s a 2013 Equinox purchased 11/12, currently has 25k miles. Out of habit I check the TPMS readout every day, the tire pressures were 33 - 34 PSI the day before. The tire went flat overnight so it was sitting on the flat no more than ~8 hours. As wesw suggested I originally jacked it up to take the weight off the tire, then I figured I might as well drop it off at the tire shop on the way to work.
The shop takes the tire off the rim to do an inside patch and then remounts and balances it. The shop has a good reputation and would not have repaired the tire if it did not pass their inspection. I remounted the tire last night and as of this morning it is holding pressure.
I’ve had more than my share of flats this year (2003 Taurus, 2010 Cobalt, and 2013 Equinox) and each time the donut spare needed air. The worst was the Taurus where the spare was down to ~15 PSI. It looked like it had never been out of the trunk. Even the Equinox spare was ~40 PSI instead of recommended 60 PSI. I’m going to get into the habit of checking the spare pressure on a regular basis.