sicky, how long it takes depends entirely on you - both how easy you find it, and whether you want to scrape through or understand what you're learning.
Frankly, 7-10 hours is incredible. I don't find learning difficult, but I'd still want at least 20 hours per exam. Then again, I wanted to understand it rather than just pass it and bin the knowledge.
Pick up one of the books and have a look at the volume of information you need to learn. There are groundschools for PPL learning, but if you're sufficiently self-motivated you shouldn't need one.