There are many recipes for egg nog.. and a good one, whether made in advance or on the day it is to be druink is:

20 eggs well beaten together and stirred togethere with 2 lbs of sugar. Into this mixture pour 1 1/2 pints of Jamaica rum and 2 quarts of brandy. When the whole has been well mixed 5-6 quarts of cream[or of cream and milk of half and half] are slowly added and carefully stsirred to bring the mixture to velvet smoothness.

Once mixed, it is poured insto a large open crock, covered with a cloth, and left untouched in a cool place until the proper day arrives !