A good UPS will provide sufficient power for your home for at least 10 minutes (and probably longer). It's not a matter of how long the UPS will last, but how long you can be without power. A UPS can provide more power than you need for the duration of the power outage. If you have a generator you can always turn it on to provide power for a short time.
You should never be without power for more than a few minutes at a time without some sort of backup power source.
A typical UPS will be able to provide power to your home for at least 10 minutes. The only way to determine how much longer you will be without power is to run a simulation.
That being said, you should never run your home on a UPS alone. You should have some sort of backup power generator.
A UPS will not provide enough power for your home for very long. In some cases, it may only provide enough power for a few minutes. The typical UPS is rated for 10 minutes, though.
For example, my UPS is rated for 10,000VA, which is 1.3 kW (1300W). It has a battery that can provide about 200 hours of power, and it has an inverter that can provide 20,000 VA.