Time attack simply means you drive fast as hell to be the fastes guy in town? (race against the clock)
If yes I would take this approach:
Set-up portals in the game.
These portals are invisible models which reach from one end of the street to the other one, so the player has to go through them (he won't notice).
Give thoses portals a negativ push value, and use IGNORE_PUSH in the player's movement instruction.
Now, each time he passes through a portal (event_push of the portal) you count a var one up (or whatever).
At the finish line you have a modified portal, which checks if the player passed through all portals.
If he did, stop the time and reset the portal count (next round)
If he didn't, do nothing as he is trying to cheat
