Every of the GS-15s I have known have had to fill out time cards, and could not log more than 40 hours per week on said card. Any time logged beyond 40 hours had to be approved as compensatory time. You cannot leave early to pick up your kid unless it is noted on your time card. The time you take for lunch is pre-negotiated and logged on your time card.
Now, I have only known GS-15s in the DoD. I do not know the policies of other organizations. But I was stunned how they treated one GS-15 who ran a multi-billion dollar weapons program. He was working his butt off, jetting off to DC to brief generals, then back to the office for a meeting with contractors, and if he left work 15 minutes early to pick up his kid from school his cell phone rang from the SES' secretary to accost him for his lack of integrity in his time card, and how important that time card is, and how they audit those time cards, etc.
The only white collar people I know who have to deal with this are lawyers with billable hours, and professional services employees who are billed hourly.
That is because white collar private sector employees are on salary and don’t get paid for working more than 40 hours a week, which they almost ivariably do. This guy shouldn’t cheat on his time card. If he has a problem with that he can always quit, but he will not. There is a reason governemnt employee turnover is very low and it is not the long hours, low pay or ardous conditions they endure.