Christmas cake

[Mairzydotes]

I have a favourite recipe for a rich Christmas cake which I normally cook in a 10" round or 9" square tin. However my son has moved out, so I would like to make the same recipe, but divide it between two 7" round tins, one for each household. As someone who is mathematically useless (although a member of Mensa) I have no idea how to adjust the cooking times and temperatures. HELP PLEASE

[wolshouse]

Delia quotes" An 8 inch round tin or 7 inch square tin. gas mark 1, or 275 degrees (140C) lower shelf of oven for 4� to 4� hours (don't open door until at least 4 hours have passed)"
Not sure how that would apply to 2 cooked at the same time - longer I suppose.
She gives 6 inch tins, 9 inch and 11.
6 inch takes 3� hours, 9 takes 4� and 11, 5� hours.