Hardening your flowers is something that should be done but not in very case. When I was a kid you would never think of designing with flowers that had not been allowed to drink water and then put in a cooler to harden. My, sister and I along with my Mother use to enter flower arrangements in a local garden club show. One year my sister made a beautiful arrangement and it came back with a note that the flowers had not been hardened properly.
I harden all of my flowers but it really is not necessary to do every time. While you can put flowers in a vase or even make a hand tied bridal bouquet ahead of time, if you keep it in water, they will last, but flowers in floral foam will not last as long. With all of the DIY weddings going on I doubt that they have the proper type of cooler to store the flowers. When designing a boutonniere or a corsage, you really need to harden your flowers and it cannot be done in your refrigerator, before or after. I cut a lot of my greenery that I grow to use for corsages and boutonnieres and you really need to know what will hold up and what will not. Preparing your flowers takes time and knowledge, I’ve been doing it for 30 years and I am always learning.