Our 300ZXTT has a system which syphons oil through the turbos even when the car is off as long as the turbo is spinning (which can be a LONG time) which IMO is the best way to have such a system. My Talon says to let the car idle for 60 secs on the visor, and I do it if I've been boosting hard or on the freeway just prior to shutoff. Otherwise I don't bother.
I never made any special concerns to let the Z idle before shutoff, however, and the turbos have been boosting perfectly and reliably for the last 10 years. I personally think turbo timers are a waste of time, but if I put down big money for a 16g or whatever I'd be sure I'd be off boost for the last few minutes of my trip.
