Originally aired on July 3, 1976 - the day between the two-hundredth anniversary of the Second Continental Congress' approval of the Lee Resolution officially declaring America's independence on July 2, 1776, and its formal approval on July 4: right between the US's "true" and its "official" Independence Day.
Notice how at one point, the colonist who reads the newspaper says, "No comics?".
The little girl who recites the "with certain unalienable rights" part of the Declaration is made up of different takes, because the girl who recorded it had a little difficulty with the word "unalienable".