WOW10 didn't work, so I went googling and found TIETHEKNOT and got 20% off. Further googling did not reveal the expiry date.
As everything in my bag was full price and it didn't occur to me to add a test product, I have no idea if it works on sale items. If someone else tries, I can update the post.
Sorry OzBargain, I really did try to get all the information before posting!