This is one of those issues where you need your boss to resolvec it. I'd request a meeting with your boss, explain how and why these interruptions cost the company money, because you need to refocus after every interruption. Give examples when this happened.

If however, you have a boss that will interpret this as "Yeah, I haven't really worked much because I constantly talk to my colleagues.", it's going to be hard to introduce these quiet hours now. Highly depends on if your boss wants to support this.