For this one you will want to be playing "Bomb Defuser", and you will need at least five people before a match can be started. When we did it we had five boosters, and it was easy because this game mode sees VERY little activity. Either way, you want to start defusing the bomb after it has been planted at your own teams base by the other team. Wait until the timer clicks to 14 seconds left, be standing with the bomb right in your face, and the very moment it clicks to 14 you want to start holding down X to defuse. You will finish with exactly seven seconds left on the bomb, and the achievement will pop after a brief 2-3 second delay. Happy hunting, and comments and upvotes are always welcome!