I have a tutorial on Guitar Tricks called "New Age Acoustic Guitar" which breaks down some techniques similar to Andy McKee. There is even an Andy McKee style video in the tutorial that shows a progression he might play along with his techniques involved. I have had people ask about teaching a video for "Drifting" but there are a lot of things that have to line up for us to teach that on the site. There are a wealth of videos available of people playing it and his techniques are not too crazy with some extensive practice. You can check out my tutorial at the link below;

http://guitartricks.com/tutorial.php?input=595

As far as length to learn this technique; Andy McKee is a prime example of hard work and dedication. He is from Kansas, and literally sat in his room for years working to emulate the styles of players such as Michael Hedges, Preston Reed, and his personal hero, Don Ross. He later went on to expand on those players' techniques and developed his own sound. If you are not familiar with any of those players, that will get you started on the vibe and sound McKee was going for. Here are some other great acoustic guitar players to check out if you like Andy McKee;

Antoine Dufour;
http://www.youtube.com/watch?v=2J_5MByRdfw

Thomas Leeb;
http://www.youtube.com/watch?v=IqSDFa8a7xQ

Justin King:
http://www.youtube.com/watch?v=cRRF_M2T-vY

Kaki King:
http://www.youtube.com/watch?v=shYdqbJgQdc&feature=related

Stefano Barone:
http://www.youtube.com/watch?v=2YE-GPXYeTA

Tommy Emmanuel:
http://www.youtube.com/watch?v=jdt4Y2fNXOI

Lastly, the album to me that is key to this style of Michael Hedges "Live @ The Double Planet." His playing, singing, and energy on this is completely timeless and is for fans of any style of music. Best of luck, and hit me up if you have any more questions.