It's about a year on the lowest training salary, currently around £12k, but that depends on how quickly the courses progress, and how well you do. I'm now looking at starting at unit in June, and this will be over 18months since I started at the college.
When you get to unit, you go onto the student wage, I think this is currently about £18k. You will be on this until you validate, which can take anything from 1 year to 2 years. So, essentially you won't get anywhere near the £30k mark for at least 3 years, and that's if you pass everything first time, the courses run relatively timely and you validate in 18months.