Are Joey and your mom visiting just before cleaning time when your litter trays are soiled, or can they still smell that odour after you've cleaned your apartment?

Our cleaning routine is almost identical to yours and we can only detect odour when the litter trays are used or it's a really warm day and we don't have the windows open. I don't know what else you can do except maybe have any carpets and rugs steam cleaned, just in case they've urinated on the carpets because it sounds like the rest of your routine is fine