I would say two days. I know some have done longer. But if you have a frost free refrigerator, they dry out the roses. So you can try misting them. Top exhibitors have floral refrigerators.

HT: 4 days, Gemini, very fresh, cut a little tight.

Mini: 7 days, Soroptimist International, also cut a little tight.

I do cover them with plastic bags, but you have to make sure that the bag doesn't touch the blooms. Long bamboo sticks can help.