To this very day I can't hear the difference between e.g. "sit" and "seat", or "eat" and "it". I can pronounce them no problem, but hearing it? Nope, those two are the same sounds. Well, whatever, the context is always disambiguating enough.

But I can hear the difference between short/long (as in, differing in actual temporal duration) vowels just fine, e.g. in Finnish/Latvian ― although those languages kinda overextend it IMHO.