I have just had a look at History at Durham- you get 8.5hrs contact in the first year, 6.5 in the second and 4.5 in the third or something like that. My DS thrives when he is busy and under pressure so it will be a whole new way of learning for him
That won't mean he's not busy and under pressure- I really wouldn't worry about that! The low contact hours in Year 3 is so he can have time to write his dissertation- which takes a lot of time.
The contact hours they list will be the actual timetabled seminars/lectures, not the sum total: he will also have individual meetings with his module tutors to guide him with his essays and (if Durham is similar to other places) with his personal academic tutor. All his tutors will have weekly office hours. There will almost certainly be extra lectures he can attend outside of his timetable, some of them by famous scholars. There will be societies related to his subject and there will be careers fairs.
He will need to be a little bit proactive and find out what there is, he will need to make use of what there is- and above all, he will need to keep any appointments he has made.
Some of the 3rd year students (RG uni, not Durham) who wrote their module essays for me last semester had weekly or even twice-weekly meetings about it which never showed up in their timetables. Others only saw me twice outside of class, to fix a topic and for a check-up. It was about what they felt they needed. This semester that cohort will be writing their dissertations- again, we'll be seeing them very regularly, but on an individual basis.
It is a big adjustment but he will get help to make it.
I haven't got the experience of a child applying for Oxbridge, but my dd had to apply 3 years in a row to get in to drama school (yes, it really is that competitive). The good news is it strengthened her resolve and made her think more about what she wanted out of it rather than what similar friends expected her to want.