right abbreviation for minutes, hours : mins,hrs OR min,hr?
What is the right abbreviation for minutes, hours?
mins,hrs OR min,hr
Is there a difference between tenses : Adjective and nouns?

ex) This is a [30-min/30-mins] class.
It will take [30 min/30 mins].

This is a [2-hr/2-hrs] class.
It will take [2 hr/2 hrs].

Question

right abbreviation for minutes, hours : mins,hrs OR min,hr?
What is the right abbreviation for minutes, hours?
mins,hrs OR min,hr
Is there a difference between tenses : Adjective and nouns?

ex) This is a [30-min/30-mins] class.
        It will take [30 min/30 mins].

This is a [2-hr/2-hrs] class.
        It will take [2 hr/2 hrs].

Answer

When you make any plural noun or noun phrase into a modifier (placed before the noun), it becomes singular.

So "a class which lasts 2 hours" would become "a 2-hour class".  It would be the same for any other duration e.g. "a 4-year course".

I have to say that it would be unusual, in my experience, to write "a 2-hr class" or "4-yr course" but I couldn't say that they would be wrong. My preference is to use the full word when it is used as a modifier.

Answer

This is a 39 min class.
It will take 30 mins.

This is a 2 hr class.
It will take 2 hrs.