5 days, a couple years back we had an ice storm that knocked power off for as much as 8 weeks for some and that was in zero degree weather.
everything froze, it took months for things to get back to normal. It was -20 for a few days during that whole thing also. Fortunately I have a 12,000 Watt LP generator hooked into my house wiring so it was business as usual for me.
Also, the best insurance against power outages is to buy a generator. What this really means is that once you have a major power outage and then go buy a generator, you will not have another major power outage.
I have a 6500 watt portable gasoline unit that plugs into a manual transfer switch. I've run all 6 15A circuits (not to max load) and the generator barely noticed. It is set up to run the gas furnace, power vent gas water heater, sump pump, 2 lighting circuits, and a couple fridges. I can always tap the 20A receptacles for space heaters if the gas isn't flowing for some reason, or to share with a neighbor.
Back in 1984 I purchased a 5KW Honda and a 5KW Yamaha generator to build a large custom home in a rural area. The Honda die and was non repairable by the end of the job. About the same time, I had a 7.5KW propane generator with a built in transfer switch I took off of a job. Finally, I had a 6KW Coleman generator my brother bought new, filled it with gas to make sure it ran and let the gas go bad. All three of the generators were in the building in Utah. I figured all of them were bad from sitting so long. When I went with my daughter to see the project up there I was surprised to see the contractor using every single one of them.
They either don't buid them like that anymore or the contractor was real handy? I run mine once a year and run out the gasoline as well as drain the carb. I know some guys who think it's better to keep the carb wet so things don't dry up and leak.