My usual policy on the freeway or in the mountains is that when I come into the exit/rest area I decelerate in "overrun" (in gear, no throttle) all the way down into the pull-off, down-shifting as required to keep the engine pumping air with no fuel being injected. That cools the turbo pretty good. Then, once I get into the parking spot I'll let it idle for a couple of minutes before shutting it off. Ditto if I'm driving "spirited" on back roads or something; around town I don't worry about it.
I don't have an EGT gauge on my Jetta; when I had my diesel boat my policy was not to shut down (except in emergencies) until EGTs were under 400F; I had pyrometers on her. It took several minutes (typically 5 or so) for that to happen coming off "fast cruise" power (on a boat "fast cruise" is typically 75% output or thereabouts.) Same deal in that case as we have on these cars; those were Air Research turbos and oil-cooled, no water jacket.
The 6v92 Detroits I had in my boat had a reputation for "eating" turbos; I wound up replacing two of four within a year of buying it (used) but over my years of ownership never changed another one. I suspect the reason why was that I never shut them down hot and thus never coked 'em. If you don't allow a turbo to get into surge, don't coke the oil, don't overspeed it and it doesn't ingest anything solid they last a very, very long time.