I would suggest you feed the as long as they will take it.  When nectar is
plentiful and available in your area, they will likely stop taking the
feed, and then you can stop feeding them.  When the nectar supply dries up
they will start on feed again likely.  Make sure you are medicating the
feed, as long as you are sure you won't be eating any honey this year.
Other wise, don't medicate.