As soon as you get to the marker, a timer will appear that counts down from 1 minute and 40 seconds. Get in one of the vehicles close by and head for the vantage point. You should have plenty of time to get there and when you do, you'll find two enemies guarding the spot. Kill them, then go to the point.
For this next part, you will need to use your camera to identify Oliver. Just wait until you see a helicopter approach and land, as well as some vehicles drive up and park. Oliver will be in the second vehicle and is indicated by a blue marker over his head. Keep watching until you finally equip a sniper rifle, which will have unlimited ammo.
You need to shoot the one guard who is pushing Oliver towards the chopper, then you can start shooting all of the other enemies in the vincinity. Oliver's health will appear at the top of the screen, and if it is completely empty, you will fail and be put back to the spot before you start shooting. The sniper rifle you have is a one-hit kill anywhere, so don't worry too much about headshots.
Keep an eye out for enemies as they move towards Oliver, who will begin moving towards the boat at the end of the docks as you take out enemies. When Oliver goes down the stairs and to the second section, enemies will start coming from the buildings. If need be, make use of the conveniently placed explosive barrels. Once Oliver gets on the boat, you need to jump into the water and get on it yourself, where you will man the turret.
Now begins the part where you kick some butt. Oliver will be driving and you'll be shooting, which can be slightly difficult with all of the motion going on. You will be taking out enemies on foot, trucks, boats and even a helicopter at the end. Keep an eye on your health and try to aim your shots carefully enough so you actually hit something. You will want to hit the men on the turrets of the vehicles first, as they will be the most dangerous. Once this part is over, so will the mission.
