I'm not a native english speaker either, but typically, in American usage, "office hours" refers to published, allocated hours for someone, such as a professor

I'm not a native english speaker either, but typically, in American usage, "office hours" refers to published, allocated hours for someone, such as a professor at a university, to allow walk-ins where (s)he can answer students' questions 1-on-1 above and beyond the classroom hours. I guess this expands to other settings too.