Were working hours always 9-5 until 20-25 years ago when it changed to 8-6?

Dolly Parton sang about working 9-5 and how it was making a living.

9-5, 8 hours for 5 days, 40 hours a week.

Then, in accounting, it’s not 9-5. You’re expected to stay in the office from 8 to 6. Why did this change? I’m not a morning person, so I’d really like to start at 9.