In my opinion, you shouldn't medicate for nosema in the spring unless the bees show obvious signs of nosema. You do need to feed a package right from the get-go until they stop or drastically slow down on taking the syrup. Go ahead and install now, since keeping them in the package won't do anything for them. If you can, insulate the hive... oh, and when it turns cold tuesday, remove the syrup if you're feeding it on a hivetop feeder, but make sure they still have some source of food. Nothing kills bees faster than cold combined with cold wet syrup dripping down on them. Well, nothing except me keeping a hive closed up on a hot day, but that's another story.