No more than one minute should be allowed for grazing. The object is for some of the plots to be totally eaten up while some are partially eaten. Usually, at the end of the grazing period, some plots are bare, some have forage and others have only the plants left that were painful to graze. The point can be made here about overstocking, that when the forage runs out, the animals can not survive. Selective grazing, lack of rest and overstocking are critical issues for healthy range and grassland.
Selective grazing is how animals pick out the plants they like best to meet their nutritional needs.
Therefore, continuous grazing has its limitations unless stocking rate is very low. The solution is to divide grazing units into multiple pastures and rotate grazing animal. That way each plant can rest on a regular basis. With continuous damaging grazing to certain plants, the ones that do not get overgrazed will dominate. They will get weak and die because they can not produce their own food.