How do I use fully automatic cooking on my Belling Built in oven?

I have the 60cm Gas Built-In Oven with Programmable Timer.

When I try to set the full automatic cooking timing function (so delayed start), the oven starts straight away.

It is driving me bananas because I want to set a Turkey to start whilst I am out tomorrow.

The instructions also don't say when to turn the setting on to conventional/fan oven at all. They just say to put the temp on at the end.

Please can anyone help?

PP
December 2013