Its not that critical. make a smaller batch to see if you can determine any benefit or not. All foods start losing enzymes right after becoming ripe and or picked/cut. But not so dramatiaclly as to have the diluted juice drink be considered seriously devalued after a number of hours. The benefits of diluting the grass juices has been found by many of us to be a great adjunct to straight up.
Better to keep the evan imperfect juice tonic going in than not. Dilution is a supreme way to permeate ones system . Drinking the fresh and refridgerated grass juice tonic, 8 oz ever hour, goes thru a gallon fairly fast, fast enough for the losing of enzymes not to be a concern, and drinking more than that at one time is commonly considered excessive and wastefull due to our systems capability to process.