When you reach your 18th birthday, we'll give you a car. - Can be an instant.
When the sun is out, it's generally light. - Can be an extended time.
When I was young ...
While you are still in school we expect you to study. - Usually a duration, extended time.
While you were gone, we voted you out :)
While I might try to answer this, you must be the judge of quality? - Not time related. meaning - "understanding that" or "even though".