What? Every single major power outage on this list https://en.wikipedia.org/wiki/List_of_major_power_outages has taken between a day to a week to diagnose. You can read about the list of detailed theories if you click through to any of them, here's an example: https://en.wikipedia.org/wiki/2020_Sri_Lankan_blackouts

Even your minor power outages take 30 minutes to an hour for your local power company to determine what failed.