Hardly earlier than hardly any grammar

The use of commas in conjunction as often causes great difficulties. That's why I've written down the most important rules here:

When the conjunction as one subordinate temporal clause (i.e. a sentence with subject and verb), a comma must always be used:
It was getting dark by the time I finished work.
When I was about to leave, the phone rang.

If as one subordinate comparison set (i.e. a sentence with subject and verb), a comma must be included:
She is better at math than he ever will be.
Canaries are a lot smarter than you would think.

But if the conjunction as comparing between clauses there must not be a comma:
Paris is bigger than Vienna. [But: Vienna is currently growing faster than Paris grew in the 1980s.]
That's easier said than done. [But: I say this much easier than I actually do.]

A more detailed explanation with as always stands without a comma:
As a child I was very athletic.
As a good friend, I advise you to quit.