Like any engine, they prefer trips long enough to get everything warmed up properly, and diesels tend to not really warm up unless they have to perform actual work.
Don't know if the small diesels are the same way, but in Class 8 engines supposedly the rings aren't even meant to seal at idle. There's a reason my '17 only has 11 idle hours on it.
If at all possible, I don't start any engine unless I can put at least 20 miles on it (get it warm), but the Ram generally gets a minimum of 300 miles on it, towing, and sometimes up to 1,300 or so.
It obviously doesn't get a chance to cool down while getting fuel, and it's not unusual that the return trip after a 1,000 mile tow begins within a couple of hours.
And by towing I mean combined weights between 20,000 and 39,000 lbs., in hilly terrain, and doing about 80 mph whenever possible.
Yes, my 3500 may sit for several months, but when it gets started, it gets to work.