I'll be the least experienced person to answer this question. But I do sell fondant covered cakes and wedding cakes and make all family wedding cakes.
When I was deciding on fondant brands, I tried them all. I made box mix cakes and covered them just to see how they each were different. Like every new ecorator, I would leave my creations on the counter, one time for a month.
Obviously the cake wasn't deteriorating. All of the cakes kept their moisture as edible over the week except the Wilton. The brand I chose also happened to stay soft the longest, Fondarifif/Duff's.
I only cover with fondant about 12 hours before the event because I have scratch cakes that many times have perishable fillings, but I do know the fondant lasts longer than the cake. I do box my tiers and cover with the large size plastic wrap, many time then to the refrigerator. No problems.