You could simply ask your current HR about their policy on this. If they confirm, then you know your boss cannot carry through on his threat. If he tries the threat again, then report him.
I've worked a 9/80 schedule at two different jobs. We were encouraged to schedule personal stuff on Fridays, such as Doctors appointments. The three day weekends were like having a mental health day every other week. And perhaps best, Fridays were declared no meeting days at both employers. The Fridays at the office were quiet, pleasantly productive days.
I used to work for a large company where we used to get a lecture every year from the company's intellectual property lawyer. The point I remember is this. If you want to protect a copyright, you have to protect it everywhere.
If Rowling wants to protect against "Gary Gotter and the Goblet of Glaze", then she has to protect it against unauthorized encyclopedias as well, no matter how innocuous or well intentioned. This provision invariably makes the big guy look bad.