they backfill when they have no queen. they have nothing else to do. by all means, make sure that your new queen will have a place to lay. also, do not be in a rush to release her. i have left them in the cage for as long as 5 days (forgot about it) and all was well. make sure the candy end is up so that it does not get blocked by any attendants that die in the cage and then wait for a bit. if they don't let her out, you can do it in a few days.
if you release her, make sure you do it down in the hive so you don't have her flying off of dropping in the grass. pull a few frames, stick your hands down in there, peel off the screen on the box , let her walk out onto a frame that is not all honey, and then very carefully put the hive back together. if there is no screen or if you don't want to peel it, pull the plug on the cage and put it back on a frame that is not all honey and let her walk out.