You'd be surprised how long fish can live in bags if you pack them right. Back when it was warm, I shipped some young severums and they were in the mail for 4 days. No DOAs. I think the trickiest part about this time of year is the weather -- nothing kills them faster than the cold. Most heat packs only last 24 - 48 hours. Aside from that, if the bags are thick enough (to prevent puncturing/leakage) and you have a good water to O2 ratio, they do remarkably well.
I'd turn the lights off and give them a couple days to recover before you try and feed them or do much with the tank. That should help minimize the stress.