I have made 100s of b'cream cake in central CA and not had the problem that video shows!
Yes, it does matter exactly which recipe and how hot it gets but as my pix show many a cake has survived outdoors.
I highly recommend this recipe:
I once set up a wedding cake (at the bride's insistence) something like 10 am in the bride's front yard - not a tree/shrub or other shade around. I learned much later that the reception didn't happen until around 4 pm. I was told by someone who attended that the cake was a 'bit dry' but didn't melt or have any other problems.
Quote from dayti:....... suggest that you/the school find a way to provide some shade for your cake, or, have them bring it from a cooler indoor spot to outside for the display at the last minute......
Totally agree w/this advice