3 prong hiders should still be timed. If you have a passage pointing down, you will get a lot of dustup shooting prone. I say point it upward, with a prong in 6 o'clock.
Don't use alcohol to clean muzzle threads, it's not a strong enough solvent. Use brake parts cleaner or carb cleaner and clean inside the valleys of the threads by scrubbing with a toothbrush or preferably a brush with phosphor bronze or brass bristles. Make sure the threads are fully dry before applying Rocksett.
Does timing of the brake need to be perfect or just relatively close? It seems from the video that you were more concerned with proper torque than exact alignment.
For suppressor performance, no not really. But its still nice to have the brake properly timed on the of chance you do have to shoot without the silencer.