Start this challenge and just over three quarters of the way there is a tunnel. Go down the tunnel and the timer earns three seconds and you reach a red flag, unlocking all time trail challenges. Note: this will not work during story mode.
When you touch the flagpole at the end of the level fireworks will appear when the last 2 digits match (11, 22, etc.). The number of fireworks depend on the last 2 digits. 11 is 1 firework, 22 is 2 fireworks and so forth.