There are too many variables to answer this, but I have some thoughts.
I don't like to graze a pasture down too tight as it will do permanent damage to the plant roots, so you really only have a few inches to graze. Three acres is barely enough for 4 cows in most cases.
Is this pasture green new growth? If you repeatedly re-graze new growth on a perennial pasture you will also do permanent damage. Regrowth will start 3-4 days after grazing and you don't want them coming back and re-grazing the same plants. Even an annual can be killed before it matures if you don't leave enough leaf to recover. Of course, if this is an annual and it has already seeded out, it won't hurt to graze it down since it is already dead or dying. Grass that mature won't have much feed value so I would not put in cows that need to gain. In that case I would graze the early breds, assuming they are in good condition.
What is the temperature? Even with moisture most grasses won't regrow in high temperatures. (85+) Without seeing the pasture or the cows (in person) I don't know which I would put there. It may not matter. I would not leave them in for very long. I would watch it and as soon as the grass looks like it is getting to be shorter than 4 inches on average, I would pull them off and move them to another pasture.