[ledge]

្The /I/ in "hit" and the /i/ in "heat" are two different vowels.

When linguists say that a language has minimally contrastive vowel length, they mean that a single vowel can be pronounced with either a short or long duration, resulting in totally different words.

So in Khmer...

យឹត /jɨt/ means "to scold"

and

យឺត /jɨɨt/ means "slow"

A long vowel is indicated typically in the IPA either by doubling the vowel symbol as I did above or by placing a macron on the vowel (a line over the top, as in /ā/).

As was mentioned, the terms "long vowel" and "short vowel" learned in English class are misleading and bear no reality to the duration of English vowels.