I would say that if you're doing the University of London BS full-time (4 courese), it's completely equivalent in terms of time required to full-time study in the US. So I think that's about the right order of magnitude.
There are exam centers all over the place, even Wyoming has two! You only have to go there for the exams in May. There is a link below with this year's exam schedule for the CS exams, just to get an idea of the timings.