In this case, I feel you will be good to go. Leaving the filter unplugged for five hours is questionable, though. When you restarted it, did you get a reall strong odor like sewer gas? That would indicate trouble, if not I would feel better about the bacteria. Since it was a fully functioning tank, there would be lots of bacteria spread all around the tank, not just in the filter. So if we assumed the bacteria in the filter was lost, you would still have lots of bacteria to support just one fish. For the bacteria, there is likely to be lots of decaying plant matter to let them not die back much, if at all on that count.
One fish is not a big bio-load! But when starting and when there are questions, it is always a good idea to test for ammonia and nitrite a bit more carefully than later.
Test, watch and have a water change ready if you do see trouble. Do it sooner rather than later. We sometimes see folks post that they have had a problem for several days and then they are asking what to do. Much better that you are asking now rather than when the fish begin to die.