Depends on the birds.I have had hens separated to three days to a week and not be challenged.You won’t need to do a completely new setup to reintroduce,just sit them in the run and if their gonna fight just let hen settle it.Lots of times,lower ranks will challenge but not always.I have had injured birds separated for days and bring them outside while they still are weak,to get some grass and sunshine and birds still won’t fight them,depends on how long their gone,and depends on the place the bird is in and the flock itself.Soemtiems when one bird starts a scuffle,one or more will join in,either to break it up or to beat up the the bird to knock it down a few notches.