Anyone doing 120 credits is effectively doing full-time study. I think the modules would almost certainly overlap at least partly - in fact, since they seem to be shifting ever more towards October starts, I suspect they'd run in parallel the whole way through - but since full-time students in a brick uni generally would be studying more than one module at a time, I imagine that's not seen as a particular issue. Could be awkward right at the beginning if you need to have done one of your Level 1 modules in order to be able to do the other(s), though - I s'pose it depends on the subject.