All of our Brit custies are 6 weekly, I tell them when we start that we can be upto a week late for different reasons, but not to worry, we will get to them. Had 1 custy that asked why we were 4 days late once.
New custies just want to know if you will be back I suppose, and not just some cowboy that is trying out a way of earning a few bob. It has to be pretty bad weather to make us a week or more late.
Had a 3 week period in Febuary a couple of years ago where it was minus 20c, but otherwise no real probs.