You can make cake batter ahead of time, but there are some caveats. It depends on the cake mix and the methods you’ve used. If it’s a mix that contains a lot of air, like a chiffon sponge or Genoise, then storing the cake batter can be very difficult, and they are best baked as soon as possible. However, if the cake mix is more like a brownie or regular sponge cake batter, then it should last a bit better in the fridge or freezer.