For this achievement, you'll need to be playing "Marseille" in Career or Projective Mode.
Make sure you have a character with good Grind and Manual Balance.
You'll first need to kill the clock down to zero and once the timer runs out you'll need to start a combo and hold it for at least 30 seconds to unlock this achievement. You do not need to land the combo to unlock the achievement.
The best place to get this is to start by doing a slow grind around all the bowls, until it becomes very hard to balance, then switch to a flat land manual, and hold that for as long as possible.
Please view the video for the best location to get this achievement on the map!