It's been hot here... really hot here... with heat indexes near 120. And as I have posted and reposted from others, heat and buttercream do not mix, and even with a fondant cake, things start to go south the longer a cake sits in the heat. So I offer this piece of advice, have the photographer take pics of your cake as soon as possible, whether it is an inside or outside wedding. Even do your place-your-knife-on-the-cake picture as soon as you can. Why? Because you never know what can happen to a cake from the time it is delivered to the time it needs to be cut.
But if the cake is supported correctly, what can happen... LOTS! Obviously, one of the biggest culprits is heat... no matter how chilled a cake is, it doesn't take much time even in mild heat to start to soften which can cause sagging, leaning, and decorations to fall off. Then there is the human factor... Uncle Jerry is enjoying the music and some drinks and whoops... there goes the cake. Let's not forget about those little munchkins who love everything sweet and may decide to sample the icing before it is time!
I am sure we have all heard of or even a seen a cake not make it all the way to cake cutting, so just get that photographer over there! At least you will have good pics!