In today’s peach climate an early peach is probably considered anything earlier than about a week before Redhaven. At least that’s how I’d answer.
Generally speaking, the earlier the peach, the more prone to split pit. If the tree has a low fruit set, that compounds the problem substantially. One way to mitigate split pits on early varieties is to make sure the trees are not over thinned.
This is a double edge sword because early varieties won’t size and build as much sugar unless they are thinned hard, which induces more split pits. We generally go for the heavy thin option and deal with the split pits. On early varieties we sell split pits as long as they aren’t open. If they are split that the top allows air/water inside, they get tossed.
You can spot a split pit pretty easily, even if it isn’t open. They have a kind of bulbous look to them, but it doesn’t hurt anything as long as they aren’t open.