My current workplace has an official policy of flexing hours for salaried employees. Which is exactly what you just described: if you work time outside of your regular hours, take comp time off for it. And my supervisor is probably the best boss I’ve ever had, she’s super respectful of our team’s time and work-life balance so we don’t even need to run flex time by her. As long as we mark it on our calendars we can just do whatever. A good boss makes such a huge difference.