Hi Cath,
It has to reach the E.Post by first post Thursday.
Therefore either post it second class post on a Tuesday or first class post on a Wednesday, so that it arrives Thursday morning.
If you post it on Saturday it will be right at the bottom of the sack of entries.
Our family has won a few times. It's a lot of work (enjoyable)for a £10 voucher!!!
I'll watch our for your name among the winners!
Blessings