Most don’t need to worry about too early especially with heavy set. I’ve only had issues once with too early and too heavy and that’s when I really went overboard with too heavy as soon as the fruits were obvious.
I’ve never had issues starting as soon as you can tell the biggest fruits from the smallest. Leave the biggest and thin to standard recommendations. I seem to thin more than standard and haven’t had issues with split pits doing that.
My “problem” with standard spacing is that it doesn’t seen to account for the small shoots and spurs. I haven’t measured but if you add all those up and leave one peach for every 8 inches that seems like way too much fruit to me. I think maybe they mean every 8 inches on bigger shoots and ignore the really small shoots. Plus no fruit on those small shoots as they can’t support the weight anyhow.