I'm surprised at the strong feelings on here about Sunday knocking. From a custies point of view you've only taken 30 seconds of their time, not ruined their life!
I never work a Sunday simply because I don't want to. However, if the price was right and a custy asked me to do a job on a Sunday due to traffic/parking/access then of course I would.
In fact thinking about it I did a school on a Sunday a couple of years back because I'd been on hols for the half term, came back on the Saturday and only had the Sunday to fit it in before it opened on the Monday.