Guys,
The answer is "there is no single answer".
On start up: What is ambient temperature? If below 40 degrees F, was a block heater on? Do you have a 4 mile drive at city speeds or are you parked on a freeway entrance ramp?
On shut down: Did you just climb a 4 mile 6% grade and pulled off at a "scenic overlook"? Or did you drive on city streets for 2 miles, pull into a CG, check in and are now at your site?
I NEVER have a set "how long to warm up" or "how long to let it idle before shutting down". I look at what is going on and make a reasonable decision.
Common sense should dictate.
