Personally it took me about 15 hours to do, with me playing around with it. I knew must of the stuff and just skimmed back over it and practiced between videos. I think you should tkae as long as you need to watch videos over and get your techniques right. You can also bookmark videos next to where you watch them it says "Bookmark" and you can view your bookmarks by clicking "Bookmarks" right next "Account" at the very top of the page.

Yours Truly,
Logan

P.S. Good Luck ;P