If you're scheduling listings to start during the time they say the servers will be offline I think it's safe to say that they won't start at that time.
I don't know how it'll work when the servers come back online, though -- maybe the previously scheduled listings go into a queue and they catch up, I don't know.
It might be a good idea to schedule your listings to start before the servers go down, or -- if you don't want to see any missing pictures -- after they're back up.