quick question: bbc's easy vanilla cake for 2 x 24cm x 35cm tins

[mumbug]

I'm doing double quantities of this cake to be cooked in 2 x 24cm x 35cm tins.

Would you cook two cakes at the same time, one shelf above the other, or would you cook and mix them separately, one after the other?

With a fan oven, I'd do both at the same time if the time if the shelves will go far enough apart.
Mum's old gas oven, and I'd do them seperatly! The higher shelf is hotter enough to make a difference on 10min biscuits, would hate to think what it might do over an hour!

yeah, i'm doing them one at a time!
have an electric fan oven but don't trust it
thanks