It's probably not a matter of the bacteria all dying at once, it's more
productive to think in terms of a decimal reduction and the amount of
time it would take to get to that point. That said, I'd be very
surprised if a couple of hours didn't make a lick of difference- my
guess for nitrosomonas, nitrobacter, and related bacteria is that they'd
probably undergo decimal reduction once every day at human habital
temperatures, and have nearly no reduction for a half day. A day or two
would probably take an equal amount of time for population proprotions
to re-establish themselves.

As an aside, many of the consortia (bacteria living in groups of
cooperating species that let them bend the rules of thermodynamics a
little)in your filter, like the Nitrogen cyclers, are happy to use
Nitrates as an alternative to Oxygen as a terminal electron acceptor.
(Biophysics jargon for why animals 'breathe' oxygen.) Nitrate winds up
being converted (backwards from what an aquarists' point of view would
be) into Nitrite by a huge variety of bacteria.