Has the length of a standard work day changed over time in America?

There’s that movie called “9 to 5” with Dolly Parton in it. Everyone I know works 8 to 5 which is an 8 hour work day plus a 1 hr lunch break, as allowed by law. People must have had lunch breaks back when that movie was made. Did they just think 9 sounded better than 8 or did people work shorter days back then?

Also, the people I know working for the military (civilian) only get half an hour for lunch. Do they fall within some kind of exception to the 1 hr law?