We had a few of the "see you in six weeks" brigade, we just ignore and turn up a month later, tbh its not often were spot on time for 4 weekly cleans anyway.
We did one today £65, they always used to say, see you in another 6 weeks, LOL yeah no problem see you next time!!
We try to avoid 6 weekers if possible as having everyone else on 4 or 8 weekly cleans it just messes up work diary, but as i say we probably are always a little behind so it doesnt really matter too much to us.