Cover the bowl and refrigerate for at least 1 hour. The more liquor you add, the longer it will keep — non-alcoholic eggnog should be consumed within 1 day; eggnog with 1/2 to 1 cup of liquor will keep for several days; and eggnog with 1 1/2 cups of liquor will keep for several weeks and continue aging and thickening quite nicely. (If aging for longer than a few days, transfer the eggnog to a sealed glass container or a mason jar.)