I don’t think once is a big deal but I wouldn’t make a habit of it. Sometimes (when I’m feeling really fancy) I will throw some fresh herbs in the nest boxes after I clean the coop. The coop smells lovely for about 12 hours. Then it smells like poop again. So if the lemon scent lasts longer than that I would imagine it has a concentrated chemical of some kind which is never a good thing in a chicken coop.