Mash B or Start to skip Snake standing up

Open up the leftmost locker with Y to grab the M9.

Careful not to get an alert here, as it will delay the elevator. Receiving a caution could delay the elevator if the caution doesn't end by the Development Supervisor credit Takashi Mizutani.

Equip M9 and Ration before the elevator. L ▼ 1, R ▼ or ▲ 1

There are a few strategies to getting on the elevator.

The safest and easiest method is by leaning against the locker, then move when the guard's left foot lands past the white line in the floor.

Fastest strategy can be found below

Don't forget to skip the cutscene as you enter the elevator, or the fadeout will take longer.