Most Carlton courses are between 1 - 3 days in duration. You are assessed via practical tutor assessment and written test. If you pass you get the Carlton diploma (in whatever subject you are studying). These are Guild and Babtac etc approved and will enable you to get insurance and practice. If you want to go on and do the NVQ or the International qualification, then you do some home study and build your portfolio. You send your portfolio in and if it is all ok then it's signed off. Then you come in for a couple of assessment days. One day is written tests and the other is practical assessment. If you pass those then you are all done and you get your qualification.
You have 3 years from when you start but in reality most people complete in about 3 to 6 months. It depends how hard you work, how much time you have and how quickly you can complete your case studies.
Hope this helps, Joy x