I can't really remember the way I entered it, but I think if you state one year, it should be fine. Although, in the WES form that we are supposed to send to CIMA, I mentioned the duration of study as 6 months (start date to end date). If I'm correct, they will assess your degree based on the recognition of the university (in this case, CIMA) than the duration of study. You should definitely get 1 year.
