I can't see why you wouldn't want to get them in ASAP. I'm told they can a last a week, if you spray them with water regularly, but I think I would put them in even if it was after I got home from work and drove an hour to the apiary, all the bees were home and they were my angriest most aggressive colony.
Be cautious about getting the sugar plug wet, because the attendant bees, or God forbid HM herself, can get stuck, die and block the hole. Ask me how I know...
Just make sure to take the tape off the sugar plug. It's always the details that let me down.