How long do you have to bake a baking dish that only holds 12 cup cakes?

15 minutes keep looking at it from time to time just in case it has aready cooked thank you.

15 mins won't even bake a cupcake!! A 12 inch cake pan will probably take about 45-50 mins. Look for the cake pulling away from sides of pan. Also tap your finger in the middle of the cake. If it springs back, it is baked. If it dents in, continue to bake a bit longer and check again.