[Hockey Tom]

I think the 6:00 number has more to do with the type of events held than the actual sunset (though one could argue that the formality of certain events are traditionally tied back to the relative time of the sunset). In the case of a black tie charity dinner, we might expect the start time around 6:00-7:00, regardless of if the event were in July or January. Thus the 6:00 guideline, which has its common sense exceptions as Michael has pointed out, is appropriate whether the sun sets at 4:30 or 9:30, as modern event scheduling does not vary much based on the time of year.