If you are stuck because the timer always gets you, what you need to do is save your grenade launcher and use it at the end. Fire one at the enemy and start running towards the exit. Keep diving, avoid enemies instead of trying to kill them. All you have to do is make it to the door by taking the left side and avoiding the red beams.

You need to run into the center where the big Buddha head is and go around it and you will have to get out of the center and there will be an opening.