A 617 will warm up to pretty much operating temp within 10-15 mins of idling....depends on the idle speed. My dad's winter SD idles around 900 (on purpose) and it warms up pretty quick.

Longest I've left mine running/idling in the cold was maybe an hour....when it was quite cold (5-10F) and the engine temp/oil temp did not fall below 80C.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)