You can start greening up to two weeks ahead if you use the proper techniques and anti-transpirants. There are several anti-transpirants available and out on the market. Some of the available brands are 'Chrysal Glory', 'Pixie Sparkle', 'Finishing Touch'
I knew of one shop......I always thought it would be a great timesaver. They process their roses right into vases. They take a bunch, split it into twelve stems bunches, underwater cut, use a hydration dipping solution, and put the roses into a vase of water.
Then they counted the number of vases of dozens and half dozens......set some buckes aside of roses for broken stems, arrangements, and the like.