I would think it depends on the spray you are using. Is it something at kills and repels them for a period of time? Or is it something that just kills any existing and dissipates (it should say on the bottle/can how long until it's safe to be in the room)? If it's something that also repels I would wait the period of time until it's no longer effective before returning the chins. Also make sure you wash anything around where the chins live that the spray may have come into contact with. If it's something that kills them and then dissipated in a few hours I would wait about a day maybe two, and make sure the area is well aired out so you can't smell it anymore. Also make sure anything the chins would be near or touch gets washed down before returning them to make sure no chemical residue is still there.