When I used to live in MA I was designing UPS systems. I forget now what the name of the electrickery authority who throws money at PQ problems, but the numbers we had were:
those that arent tend to be > 15 minutes.
our flywheel based system provided 11.5s of go-juice - enough to ride out the 3s outage then black-start an MG set if the power still hadnt cme back on. IIRC the 3s is tied in with the switching time of auto-reclose breakers. If you are on the branch with the fault, the ARBs will disconnect you, hence the > 15 minutes - actually however long it took to fix the fault. If you are on another branch, your supply will come right when the faulty branch is isolated.
Cheers Terry