500-600 hundred words which is roughly about 3 A4 pages. Examiners usually have your grade figured out by the end of the second page. Remember, it's all about quality, not quantity. Better to have two pages of perfect grammar and good paragraphs with strong points than 3 or 4 pages of waffle and awful grammar! Best of luck! :)
You have a really long time it's easy to ramble on and write 5 but from what I've heard you're better off with around three and a half good pages as the more you write the more you tend to stray off topic, losing marks.
I wasn't prepared for the aiste in my mocks and wrote a page and a half and got deducted 10%, my irish teacher also told us that if you write less than two pages your deducted 10% and he use to be an examiner. So I'm positive that the page count does matter once it's 2 or more pages you should be fine. The composition is worth around 16%, so you can pick up marks in paper 2 and once you feel confident of how the oral went you should be fine.