My company had several thousand vehicles during my working years, when I started working we were told to wait until the temp needle moved before driving off, by the time I retired in 1995 we were told 15 to thirty second would be adequate. The trucks we were driving were about 28k GVWR. I am like some others, I'll do what I've been doing for years. Both of my wife's vehicles have rung up over 200K miles with out major engine problems.
As far a Chum Lee's suggestion, from what I have been able to figure out it is the Cold Dry air from the AC which comes on automatically when the heater controls are turned to Defrost, not the warm air from the heater. That may be wrong, if it is someone explain why the defroster works the way it does.
To Almet, you may be joking but about those of use that hard of hearing or deaf but it is not the least bet funny. My hearing problems are a result of defending this country while operating in an area where we had no Doctors available to care for us. Please don't make stupid jokes until you put on sound deadening ear muffs and find out what it is like.
That is just my $2.37 worth($.02 adjusted for being older than dirt.