I had a horse on livery for 5 years at one stage, hoping to get another in the near future, once the finances are sorted. I was riding 5 times a week, as well as competing in eventing and showjumping. I found I spent about 15-20 hours or so with the horse (not including travel time), as we had a really social bunch were I was, and would often be nattering after our rides. Of course if I was competing, the hours increased quite a bit for that week.
HTH.