#FORZATHON Live events start at the top of every hour. They will appear on the map as a big pink circle 10 minutes before it starts, and you will get a notification on screen 5 minutes before it starts. Drive to the circle and wait before it hits the top of the hour, and you will be included in the event. Then just complete all 3 rounds to finish the event. Do this twice more in consecutive hours (Ex: doing the 5:00, 6:00, and 7:00 event) to complete the achievement.
When doing the event, please participate in all rounds. It's no fun when 3-4 people are doing all the work and 10+ are just sitting around waiting.