9-5 aren't sacrosanct. When the 9-5 song came out approximately nobody worked from 9-5. Standard working hours were 8-5 with an hour for lunch. Starting at 7 was far more common than starting at 9.

The song is about a secretary who didn't get a lunch hour, so started an hour later than her boss.

Tech workers generally start at 9, but that started decades after the song came out.