Would the horse be on self or full care? That may make a difference. Mine was on full care and I spent about two hours per day, five or six days per week, at the barn. While I did not have time to do any other committing team sports (but then, I didn't have much inclination to) or try out being in a zillion different uni clubs, I still had time for socializing, spontaneous and planned, and plenty of wild partying. I was happy with this arrangement and don't feel as if I missed out on anything. I wasn't out getting panelled every night, as some students seem to manage, but then, why would you want to?
As I said in my earlier post, it depends on what you want at uni. There are people who feel the need to really try and change themselves and join every vaguely interesting club and society and drink like fish every weekend. Others don't. In the uni mountaineering club, we get a cohort of first-years every year who have never been on a mountain before and figure out pretty quickly that being cold and wet on a Scottish mountain isn't for them. They're the "try everything" type, who soon realize that mountaineering requires a certain level of commitment, like investing in gear that prevents hypothermia. Eventually everyone becomes more settled into just doing the things they like anyway.
My current university also has a riding club, which I'm not at all involved in, but I know that it's there. They get discounted lessons at one of the local yards. I think many UK unis have such arrangements. My undergrad (US) uni had its own barn, and all the other boarders were students and a couple staff. So the barn was very much tied into the social experience. Riders were known for their particularly drunk and wild parties.