Is it a new family or a family that is currently in care and finds they just need that extra 5min? If it's a new family I would be more likely to charge just to set the precedence that your policies and rules are solid. If they have been in care for awhile and are otherwise a great family then I might let it go...if they are in care and have been making life hard in some other way then I'd charge for the 'burden' of changing your day. The time does add up and 5min can quickly become 10min...