QUOTE(corenfa @ Apr 2 2011, 10:24 AM)

I would think one would need several years worth of preparation. What happens in those years is also important, it's not just about locking yourself in a room with a piano 8 hours a day but also reading, discussion, and listening to a lot of music.
There's a high failure rate for the dip and this is probably why. Some people look on it as just grade 9 by another name but it requires a lot more musical maturity and not just the ability to rattle of the pieces by rote which with 8 hours a day locked in a room with a piano for a couple of years is doable.
Even with years of piano playing and a huge knowledge of music, musical history, the instrument your playing and so on it is still really difficult to pass.
So in conclusion it's really hard to know how long you need between grade 8 and dip. You can only judge your situation where you are now and think about where you are in your musical life.
When you look at the diploma repertoire how difficult do you find it?
How long do you typically need to get to grips with the notes of, say a Scarlatti sonata, or a Beethoven sonata or whatever?
How well can you memorize?
What are your sight reading skills like - essential for the quick study?
What is your general musical knowledge like?
How long does it take you to read and understand a book about a particular composer in order to be well versed for the viva?