Matches would be 3 hours in length. No thank you.
Extra time rough rule of thumb. 1 minute added for a goal, 30 seconds for a substitution, 30 seconds for a card administration. Actual measured time for injury.
And yes, extra time can be added during the extra time.
In HS matches, the clock stops for a goal, injury and administration of a yellow or red card. When the clock hits 80 minutes, game over.