I've done it with other cake mixes, because I have plenty of single special shapes. Cover and put it in the refrigerator. When the first cake is out, I quickly wash the pan, prep it and bake the second cake. In effect, the batter is only sitting in the refrigerator about an hour-ish and I haven't noticed any difference in the two cakes. I've never tried leaving it much longer than that, so I dont know what kind of time limit until its lift expires.
yes, it can sit; I have had to let WASC batter sit inbetween cakes before and it still bakes a great cake. 
please forgive me but what does WASC stand for?
WASC= White Almond Sour Cream cake
Here's a link to the recipe:
http://www.cakecentral.com/cake_recipe-2322-White-Almond-Sour-Cream-Cake.html
I cover my KA mixer bowl with a damp towel and leave it on the counter. I have used the same batter to make a spiderman pan cake, then two six inch cakes, then a ball pan cake. Batter was fine! I leave it out all the time!
Okay - I'm so silly. The minute I'm done mixing I'm rushing around like freaking CRAZY trying to get the cake in the pans cuz I feel like I have a ticking time bomb on my hands and now y'all are telling me I can relax a little
Oops.
Rachel
Yes, Rachel... don't risk running around your kitchen and knocking something over 
All baking powder used these days (unless specifically labelled otherwise) is known as "double-action". That means it produces leavening gases when you add liquids, and again when you add heat. (I'm pretty sure I have Alton Brown to thank for that tidbit.)
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