I toured a datacenter once back in the early 2000s and they showed me 30 days of generator fuel storage. When i asked them why 30 days and not 35 they replied "we're such a major customer of both electricity and fuel that if we don't get electricity or fuel for 30 days there's way bigger problems than your website not being online" hah.
Anyway, we had a load shedding agreement with a large bank across the street from São Paulo and we could switch over to their Unisys mainframe in a matter of minutes, and vice versa.
And if the data center is more than about 5 years old it almost certainly was not planned with adequate backup power to run racks of GPUs.
Look at data center responses from Hurricanes Katrina and Sandy. This guy [1] was onsite for Katrina. Lost utility power on August 29. They did have some access to fuel on Sep 1, but pretty spotty until maybe the 3rd. Looks like power started coming back in some places Sep 8, and maybe widely restored on Sep 14th.
I would say, by 7 days in you'll probably have a good idea of if 30 days might not be enough.
[1] https://web.archive.org/web/20061206181753/http://interdicto...
https://craphound.com/overclocked/Cory_Doctorow_-_Overclocke...
He just couldn't get past the notion that if the six copies in four buildings across two states were all simultaneously physically destroyed, then most likely there are also no more schools left standing, and hence the contracts to clean them are null and void. Also, payment is now in booze and ammunition, not dollars.
"I was in the office, reviewing Terraform plans"