There are 3 red keycards on this mission, but only 1 is needed to get the golden keycard. This allows skipping the upper left room by sniper supporting the single enemy (the other 3 enemies in that room don't spawn unless you get the keycard). The keycard is collected in the room behind flamethrower with a detonator Richard, who litterally does nothing to stop you from grabbing it and the hostages. Same thing works on the other Richard later in the mission.

Haven't found a reliable way to get the red barrel on the far right of the map to fall down and blow the shield enemy, so I use a breach charge drop from the ladder instead.

Aside from losing a second from missing a hostage, most time improvements for this mission will come from better execution.