Turbo charged engines do like to cool down after a high journey. If you drive 'normally' for the last few miles it will be fine. I tend to let the engine idle for about 10 secs before turning off. But its not necessary really unless you do a track day or run on the motorway at high speeds then stop, this is when the oil can be very hot.

After a long commute at low speeds the oil won't be hot, well it won't be as hot as driving at high speeds. This would be the same sort of driving you would do to cool the engine down.

Usually the manual gives you hints of what to do, some say to let the engine idle for 10secs before moving off in the morning.

The most important thing with turbos is the oil type. Make sure its upto spec and serviced properly, I tend to change the oil in my cars every 6,000 miles, but that just me. Modern oils take alot more abuse so gone are the days where you have to sit in the car for a few minutes waiting for the oil to cool down and not gum up on the turbo bearings. This is why some people fit turbo timers to allow you to lock the car and leave it running, then the turbo timer will turn the engine off. You see them on alot of Jap turbo'd cars like Imprezzas, but they're really just a gimmik.

Having said all this diesels run cooler than petrols anyway.

As the car is new, drive it as stated in the handbook - Gently for the first 1000 miles then gradually increase rpms etc and don't let it labour in gear.

Enjoy!!