I remember reading in Stephen King's On Writing, that the first draft of a book - no matter the length - should be finished in three months. However, I feel he's an unusually gifted writer when it comes to volume (one could argue about the content as it's not to everybody's taste), and perhaps the rest of us should take his advice with a pinch of salt!
I'm starting on an idea for my first novel and this is very helpful! Nice to know that whatever I do - write fast or slowly - is right, because there is no wrong way to do it. Thank you :)
I think that having a set goal of an amount to write each day is the best way to plan out a book. Building that habit goes a lot way in actually completing a work in a timely manner.