The last few years the chicks have come back to the box until all the sibs have fledged and then for a couple/few more days after that. Depends on the chicks in any given year. Hurricane and her sibs never came back to the box. Last year's kids did quite a lot.
Do you think it depends on where they hatch, TPC? I mean, do they tend to return more to the west nestbox more than the east nestledge because there is shelter there?
Nope, location does play a part, its all the chicks' preferences ... remember, once the chicks can fly, they can find cover anywhere. When they come back, its because they want to return, not because the box provides something they can't find anywhere else.