How do you start Showtime in Burnout Paradise (PC)?

I've configured the Z key to start showtime in Burnout Paradise. But when I press it, nothing happens. On my friend's computer, the road signs at the top of the screen are red, and he tells me that that is because he has turned on Showtime and the timed road race (don't know what's it is called.) How do I turn that and showtime on?