I have been putting out a late fall application of Urea for over 10 years now - right around Thanksgiving depending on the weather.
From Purdue's Turf Tips:
"The late-fall or November application timing should be near or after the last mowing of the year, but while lawn is still green. Typically, there may be a month or more between your last mowing and the time the grass turns brown or goes under snow cover. Generally the first few weeks of November are when to apply. Earlier Purdue research suggests that the nitrogen must be taken-up by the plant before winter to be most effective. Therefore, a quick-release (or soluble nitrogen source) such as urea, ammonium nitrate, calcium nitrate, or ammonium sulfate is most effective. The target application rate for this November fertilization should be 0.5 to 1.0 lbs. N/1000 square feet."
I've had great luck, lawns have developed deeper roots, the turf is denser and there has never been a problem with mold or disease.