I don't think miles is a good way at all to think about warm up times. Last week, I got my Sprinter up to the 190 thermostat opening temperature in zero miles. Of course, it was idling in my driveway while I was adding refrigerant to the AC.
More typical might be around 3 or 4 miles for me. That's in fairly heavy stop and go suburbian traffic, sometimes having to wait through 2 or 3 cycles of a traffic light to get through an intersection. Based on time, that might take about 10 minutes.
If you can pull out of your driveway and get right on to a highway, it could easily take 8 miles - but still be around that 10 minute mark.
As long as the engine warms up and doesn't overheat, I don't worry about it.