How long should it take to go through your books?
It depends on your playing level, the amount you practice, and how you practice.
Generally speaking, though, my books tend to pack a lot of material in, so they take somewhat longer to get through.Figure on maybe 4 to 6 months of diligent, consistent practice to really get down the material in the volume 1s of my Metal Lead & Rhythm books. (I recommend you take themboth together.) If you are coming into it with more playing experience, you may cruise through them a little faster; if you are starting from stratch, maybe longer. Don't worry about how long it will take, though. What you learn and how well you learn it is more important than how fast you progress. Also, to make sure you are practicing efficiently, read the posted info under the "Tips & Advice" menu tab.
For the volume 2s, keep in mind that you're pushing a professional playing level by that point. So figure on the better part of a year or so to complete them. I know that sounds like a long time, but you'll be steadily improving all the while, so it'll be something you're having fun with -- not a grind that you're just waiting to end!
Books like Metal Guitar Tricks or the faster paced methods like Thrash Guitar will be a little quicker. The Guitar Lessons books are probably a month each or more. The Beginning Rock Guitarvideos and booklets have a bit less material than a full-fledged book/CD simply becasue of their format. Maybe a couple months for all of them. But a book like Speed Mechanicsfor Lead Guitar or Secrets to Writing Killer Songs can be used for years.
These books take longer than most others, on average, because there is more in them. Just focus on what you're getting out of them,and how much improvement you see in your playing.