about an hour. Why?

                                  Answer:
   
   The waiting time is based on a discussion in the Talmud where tree
   different times of waiting between meat and milk are taken up as being
   valid. The base for the wait is the verse in the Torah saying that you
   should not boil the kid in its mothers milk. The question is what is
   really demanded. The one hour wait is based on the premise that all
   that is needed is for the taste to disappear from the mouth. The six
   hour is based on the time it was believed to take for meat to leave
   the stomach. There was also a twenty four hour wait, based on the meat
   being totally gone from the system, which has completely disappear as
   a custom.
   
   Note that both agree that there must be a delay, it's just that the
   different communities came to different conclusions about the length.
   It's a matter of custom. The delays selected appears to be based on
   the elapsed time between two meals in the respective societies. All
   agreed that they must not be eaten at the same meal, and "bentching",
   i.e. the recitation of birkat ha-mazon/Grace After Meals, was
   considered to be the end of a meal.
   
   German Jews wait for three hours, since a mid-afternoon snack (about 3
   hours after lunch) was common practice among Jews and non-Jews in
   Germany. No such habit existed in Poland or Russia, hence six hours.
   And, you guessed it, a late-afternoon snack one hour before dinner is
   not entirely uncommon in Holland. The valid ones today are the one and
   the six hour periods. The three hours custom of the Germans is less
   accepted; traditionally, if a boy who keeps three hours marries a girl
   who keeps one hour, the custom is that he adopt the one hour wait of
   his wife. However, if, the boy keeps a six hour wait, the wife should
   change to waiting six hours.
   
   One contributor notes that some Dutch Orthodox Jews actually quickly
   bentched (said blessings) after the meat course on Friday night,
   entertained his group for one hour, and then served a dairy dessert
   after asking if anyone objected and being answered in the negative.