Cool down time 3 mins after exiting the runway and 5 minutes if I have just done a go-around worked for me.
A couple of years ago, I was at a strip and a dude was coming and going in a Navajo. The taxiway was straight off the end with a 50 metre taxy. My mate and I asked this dude after a while why he would taxi straight in, not cool down and shutdown. He didn't really seem to know what we were talking about in regards to turbo cooling. He had been doing this for a year and had not had any turbo problems (apparently??).
What the ...?