Power outages can last for different amounts of times and it depends on how severe the damage is that caused the power outage.
Sometimes all the electric companies have to do is flip a switch and the electricity comes back on or replace a fuse and sometimes storms and other severe weather events cause major damage to power lines which then requires hours or even days or weeks worth of work to get things fixed so they can turn the power back on.
So it can take from a few hours to a few weeks for electricity to be restored depending on what caused the power outage.
It's a good idea to have a backup generator either portable or a generator that powers your whole house called a whole house generator.