The 6 moves / minute is an average. For a fast game like 10-0, you would use less of it in "memory/experience" based positions (like the opening) use more of the clock for critical/analytical positions.
For the opening, you would normally be expected to bring an opening system (not some foolish attempt at memorization of a line you will hope to play) to the table and use it to get a "playable" middle position. Anything you are comfortable with ... or even something you are not (if you are just practicing / learning it! :))
If you are quoting Heisman, you should have read his famous Two Move Triggers Novice Nook that addresses these questions.
Also, Heisman mentions the Botvinnik guideline which says "use 20% of the time control for the 1st 15 moves".
For 10-0 that's 15 moves in 2 minutes which sounds about right with the budget you just described.
Finally, if you are needing "help" manage your time at blitz, that's a red flag to "NOT" play at this time control and work on your slow game until your ability to play from "memory/patterns" is faster and more reliable. :)
I play 10 minute Blitz. If I take 10 seconds per move, I will enter 60 moves in 10 minutes. That equals six moves per minute. 60 moves is plenty to decide most games.
My problem - almost all of my games go out of book in under 5 moves, so I hardly play moves from memory. Some quick calculation and chess thinking is required.
Dan Heisman says to NOT spend time in the opening thinking about alternate candidate moves, if all three are equally good. This prevents time trouble.
So, how should I approach the opening in 10 0 Blitz? What should I be thinking about, or not thinking about? How many seconds per move?