How many "office hours" are common (or standard) for full-time lecturers?
My undergrad university held regular "helpdesks" in a classroom - where one or more teaching assistants and  sometimes the lecturer were present. They essentially functioned like an extra (and optional) tutorial class, and the more proactive students would come in and work on their assignments, discussing among themselves and asking questions.

This allows you to spread time a bit more fairly among students than at an office hour, where one student might take up a lot of time and leave others waiting at the door. Answer one question, and then move on to someone else.

Perhaps you could try a similar strategy?