Use the "Cone Crazy" side mission, found on the rooftop of the Ocean Beach parking garage (near the Ocean View Hotel). You’ll find a Stallion parked there. Entering the vehicle starts the side mission.

For the first 7 attempts, complete the mission by collecting the final checkpoint with exactly 0 seconds remaining on the timer. After each attempt, you can quickly restart the mission by parking the Stallion back in its original spot, and re-entering the vehicle.
After the 7th time, you have to collect the final checkpoint by adding an additional second than the previous time (ex: collect the final checkpoint on the 8th attempt with 1 second left, collect the final checkpoint on the 9th attempt with 2 seconds left, ect...).
Then just continue increasing your time by one second on each run (3, 4, 5...).
If you are struggling, you can gently move the cones around before collecting the checkpoints. That makes it so much easier.

In my case, I replayed the mission about 20 times, earning over $800 million and unlocking the achievement. I had a maximum of 15 seconds remaining on the timer (I tried 16 seconds, but it didn’t work).

PS: Credit to GTA Series Videos, the YouTube channel where I found this table: