They are not legal if they are built in to the alarm or immobilizer , they are tolerated though and generally the pits and police are OK with them.
ADR 25-Turbo timers are not to be fitted to vehicles manufactured on or after 1 January 1972 (ADR 25 Anti-
Theft Locks). ADR 25 requires that the normal function of the engine only occurs when the ignition
lock is in the engine on position.
You may find it difficult to find a reputable person to fit the turbo timer with the immobiliser , not because of the ADR issues but because a relay bypass must be wired into the alarm to disable it while the turbo timer is operational , leaving the car unsecured and the installer liable.
here is a nice thread , read the comments by the alarm installers in it and the stuff on bypassing security
http://www.skylinesaustralia.com/forums/topic/356357-turbo-timer-vs-alarm/