bczoom,
The JD manual says let the engine warm up for 5 minutes. What I have noticed is that if it is warm out in 4 minutes or so the coolent temp will be in its normal position. Soooo, I have modified what the manual says to do. Once the temp gauge needle is where it sits when the engine is warm, I move the tractor. In the summer it takes roughly 4 minutes. In the winter in takes more than 5.
I have the throttle set about 1600-1800 RPMS when it is warming up. I let the engine idle at 1000-1200 RPMS for a minute and then move it up a bit.
If the tractor is not being used I generally just park it, lower the FEL, 3PH, set the brakes, put two or three gear levers in N, and let her run. I want the engine to stay warm and charge the battery. Usually when I do this I'm sawing wood. I might let the tractor sit for 45 minutes or so. Remember I'm not idling the engine its running about 1800 RPMS.
I try not to start the tractor if I know I'll have to turn it off without it running at least 60 minutes. The longest I'll run it without using it is when I'm burning. When I burn the tractor does not get turned off until the fire has burned down to somewhat safe level. Usually takes 4-5 hours depending on the size of the pile and wood.
Later,
Dan