Ok, so I'm making a tiered cake next weekend, a 16x16, 12X12 & 8X8, using DH cake mix. If I make lets say 3 boxes and only used 1/2 to fill one pan. is it ok to use the remaining mix after the it's been sitting for over 40 min. This is my first time making a tiered cake and it's for a family member who is 12 hours away, so I have to make one cake layer at a time at their home. Is it also ok to bake the 8x8 and a 12X12 at the same time? Thanks for your advice.
Sure, on both of your questions. I have had batter "sit out" while I am waiting for others to bake with no problems at all. Some people may tell you to chill it, but I never did that. And yes, you can bake two cakes of different sizes at the same time. Just set your timer for the smaller cake, check it for doneness, remove and continue baking the larger until done. HTH.
On the cake I made this week I mixed two mixes and divided it between an 8" square and a 6" round. I baked the 8" first and while it was in the oven I put the 6" in the fridge. I took it out about when the 8" had about 10-15 minutes left and then baked it and it turned out just fine. I used Pillsbury mixes.
Yes to both. Those always happen to me on a regular basis.