I would not use a comma after the "Please", but the first one is correct. You cannot use off to describe the ending of office hours. If you are looking for an alternative way to write/say that sentence, I would say "The office hours have ended. Please come back tomorrow" As a side note, we usually specify who the office hours belong to. For example, if you work for a school and a student asks about the office hours, it is better to say "Our office hours are over for today. Please come back tomorrow" instead of "The office hours are over for today..." Hope this helps :)

You can say the first but not the second. Usually we'd write, "The office is closed. Please come back tomorrow."