Seems not to work! Sorry
Sorry to be a nuisance but while this worked in testing by changing the date in the code it doesn't seem to work in practice.
I now have a testing site up with dummy content and for the pat three weeks it has shown the same list without change.
This is the page index.php the list is towards the bottom on the left (picture of a ship). I've attached the code for the (entire) page.
If you haven't time to look at this please say so, I'll totally understand.