The third person gets all the keycards for the puzzle and will likely be slightly behind the other two. You don't have to be perfect, but shoot for 3 mistakes or less. This still requires some mastery of Zero Hour. Two people run normally, as fast as possible. I like void, which is this week, because it makes Guillotine hit extra hard and because the only void damage in the boss fight is from the servitors, who are gonna die VERY fast. You run through Zero Hour heroic on your singe week of choice. Each puzzle entry adds 15 seconds to the clock.
If you do the puzzle once on each singe week (arc, solar, and void) you can unlock…an absolutely hideous ship (and advance your Outbreak catalyst faster).
It's a challenging activity, though it becomes a lot of fun once you start to get the hang of it. Enemy shields are ridiculously durable with match game, the route requires specific knowledge of exactly where to go, the checkpoints are brutal, the jumping puzzles are extremely precise, and the final boss fight requires a decent amount of advance planning and tight execution. Most people consider Zero Hour to be one of the hardest activities in Destiny, especially on heroic.