I would reccomend one minute of idle before driving the car in almost any weather. These diesels are fairly effecient and don't create alot of waste heat at idle, so it will take a long time to come to operating temperature. I believe twenty minutes or so (cruising speed) at operating temp is required to remove any condensation from the oil. That figure could be pure fiction, but you should let it run on the highway as much as possible. Personally, I think any amount of city driving is horrible for the car, but in the end it's just a tool of transportation, so use it as you must.

How long are the trips you make during the day? All city driving? Maybe use the diesel in the spring, summer and fall, and use the ford for poor weather and winter driving.

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1976 BMW 2002- 100k
1995 BMW 325i 175k
1984 Mercedes Benz 300D Turbo Diesel- 270,000 mi

1981 Mercedes Benz 240D- Estimated 300,000+ mi Returned to the earth