12-15min gets me to full temp on water and oil, unless it's really cold, then by 20 for sure, remembering that I don't let it sit at a true idle.
Hmm. I'm not that lucky. As far as I know, none of my vehicles have ever built up good oil temp from just idling. They all seem to need to perform some actual work for the oil to get warm enough.
Air cooled engines could be an exception, but since I avoid idling anyway, I don't know for sure.
It doesn't get really cold here (-22 is the lowest I've seen), but then the 'Cat wouldn't be out anyway.
I should add that I've never tried idling it for extended periods, but when it's warm out (or even hot), it takes about eight miles of slow driving before the oil temp even starts showing on the scale.
To then get it over 212 requires a few stomps on the pedal, or climbing some decent grade.