Flexible hours was introduced at my insurer in 1975 when I was a manager. You could start between 7 and 10 am and leave 8 hours later. Junior staff generally started between 7 and 7:30 am in my department; the senior staff started 9:30 to 10 am. I don’t think much work got done before 10 am as insurance companies had pretty lax workplaces.
It was quite a contrast to my 1980s job at Bata Shoe. Mr. Bata arrived at the office every day at 8:45 am and woe betide any employee who was not in his/her office by then. Even senior executives would run for the front door to beat him there if they spotted his car approaching the entrance.