Will the other Friday be shorter, too? Because otherwise they’re getting an extra hour out of you every other week.
I do this at my job (my choice). I do 7 to 4:30 with a half hour for lunch. I don’t actually take the lunch when I’m in the office since there’s no place other than my desk to be, and thankfully my supervisor is fine with me just leaving at 4. When I’m at home I try to actually be away from my office for that time.
I do like 3 day weekends and when I’m WFH I don’t even notice the 9 hour days. Idk if I’d do it for a job I had to be in the office every day for, but hopefully it will work for you.
If the job requires you to be at your desk then presumably that means you have work to complete. Judge people for what they get done, not how often they mindlessly move a mouse and this wouldn’t be a problem!