Wall strafing at the start allows you to walk past Mason and McKnight to the shack but you need at least 69 (nice) speed, after the first wall strafe spam A and D to move faster to the shack. In the second wall strafe you need at least 70 movement speed to get over a small bump or you'll run into McKnight. At the airport it's best to shoot all enemies because Mason likes to slow down and shoot them or hide in cover which loses time.

Mod edit - retimed