Depending on what you have planted in the plot mowing after hatches can be good or bad. If the plot is grass-like where the plant stems are close together mowing would be a good thing. If the plot is Forbes or other flowering type plants like clover where the stems of the plant are further apart mowing can be bad.
When you mow plots with Forbes or early succession habitat to early your taking away the best brood rearing habitat available. The separation at the base of the plants allows the small polts to move freely with overhead cover and also allow the hens to watch for predators because shes tall enough to see over the vegetation. These types of food plots if allowed to grow will provide small polts with plenty of bugs to eat and cover to hide from avian predators.
Snakes and other non avian predators tend not to use this type of habitat.
If the plot is grass-like mowing would be good but it still doesn't provide the habitat needed for newly hatched polts until they get large enough to navigate over the grass bed instead of through it. I've heard it put this way; imagine a bird as big as your thumb trying to walk through your front yard. It's not going to happen so hens won't use the plot with newly hatched polts and will be forced into habitat thats less beneficial until they are bigger.