While the above solution is excellent advice, I think it is more appropriate for a legendary or LASO speed run. The par time on Keyes can be achieved by just setting the difficulty to easy and running through the level.
As early as possible, get the shotgun. Speed through the level and don't stop to shoot anyone unless they are actually preventing you from continuing. There are lots of tight hallways crowded with flood - if there are a clump of flood, use a grenade. You should be able to beat this with plenty of breathing room without using any glitches. Remember that once you found Keyes, and you're back in the hangar, you can just drop down levels by falling over the side (fall from 3rd floor to 2nd to 1st) and then immediately get in the banshee.