I wouldn't be putting on any extra hours for them- at the start of the course, I explain that there are lectures, seminars, that I am happy to see students immediately after if I don't have another lecture just for quick questions, then I have office hours twice a week and so on. That totals a huge number of hours contact time in a term, and I do expect them to work on this course with me in those hours. I also explain I won't be available over Christmas or Easter, so that all questions relating to exams/essays need to be done in the office/dedicated hours that term (unless an actual emergency). The course materials are all on VLE and very comprehensive, and I also have lecture recordings, but I don't give those out at the start of term for obvious reasons.
It has taken me years to get it right, one year I was deluged with people wanting revision advice over Christmas who had not attended properly all term, and I thought enough is enough.
I would make an exception for any students with additional needs/special circumstances, but usually they are able to make some of the many hours a week I am available or I chat to them on the phone/review work via email.
This has made it much simpler for students to understand what is appropriate behaviour, and now they all cram in my office hours the week before an assignment is due!
I have also prepared slides/sets of questions about the exam, and email them these proactively, telling them that they need to read these and look through past exam papers first, and then only contact me if the question wasn't answered by those. I also say that I won't answer any speculative 'should I revise this and this and be covered?' questions as it's unfair on other students to go topic fishing.
You would think all this boundary setting and less availability would upset the students, but the opposite is true, the course feedback has got even better and I think it's because they know what is expected of them at all times, including when/when not to email. It's also made my holidays 100% more enjoyable!