Oh, this might be the most discussed topic on CB!
Hard-boiled eggs, no issue, as there’s a bit of range in the cooking time. As long as you’re not super-picky about it, anywhere from 10-13 minutes will get me a hard-boiled egg with none of the overcooked greenish yolk. The eggs I cooked tonight for our salad were 11minutes.
Soft-boiled, another story entirely. I think I’ve made a “perfect” (by my standards) soft-boiled egg exactly once, and it was done using a particular method and at six minutes exactly, and I’ve never been able to recreate it. I suppose on that day, I had the right-sized egg with exactly the right-thickness of shell, in a room that was the perfect ambient temperature, and all things came together.
My last softie, I did for six minutes, just the tiniest bit of cooked yolk in it, but I don’t want
any cooked yolk, so when I make the next ones, it’ll be 5:45 for the cooking time. I’ll likely get the yolk I want, but the white will be too soft. I want a firmly-cooked white and a fully-liquid yolk.
That’s the best I can recommend - use the same brand/size eggs, always be consistent with taking them straight from the fridge or set out for however long you like (I don’t like to let mine sit out), use the same pan, same amount of water, same burner set the same, and then start adjusting the time in 15-second intervals, and watch it like a hawk.