How long can you keep cake batter out , before baking? i want to make 50 cupcakes......my oven is small i can make only 12 at a go ....so was thinking i could make the mixture and keep baking in batches. will the cake mixture spoil?

About twenty minutes before the rising power of the baking powder starts to decrease ...

If it's scratch, then not to long, the chemical reaction starts taking place as soon as you mix everything together.

If it's a box (or box modification) then you should be ok for awhile, but you can always pop it in the fridge while you're waiting to fill the next pan.