Interesting; this is a difference that I haven't heard clerly.  Do you
know of anywhere that tries to explain it well?

No, nowhere, which is why it took me so many years to figure it out for myself.  I remember reading in a Latin textbook back in the '70s about long and short-length vowels in Latin and their importance in word meaning, and had no clue what they were talking about.  When I started reading about ON recently I read the same things so I started analyzing exactly how I speak myself, and that's when the coin dropped.  Now, I've tried to find Scandinavians to listen to as they speak and I finally realize there is a difference.

Here's an example, which I relized from hearing Chinese people speak English in Los Angeles.  They have trouble with distinguishing words such as "dog" and "dock".  I did some diction coaching with them, and realized that the final consonant wasn't the problem, it was the length of the vowel.  When followed by a voiced consonant such as "g" , we always hold the "o" vowel longer than when an unvoiced consonant follows.

Try it, listen carefully and you'll see what I mean.  There are lots of examples you can play with, such as "dad" & "dat", "lag" & "lack", etc.  Now, we do take care to pronounce the end consonant correctly, but you'll find it's very difficult for yourself to say "dog" with a quick vowel.  The mouth and throat just don't want to do it.

Tim