It takes about 20 minutes. There are a few steps where you need to be careful or springs will go flying and you can leave scratches if you're not careful.
I put my first one together a few weeks ago and it was a piece of cake. Completely unintimidating. That said, I have a long background in mechanical repairs. There are some excellent youtube videos and web sites that will walk you through it.
Real plus on my assembly: I did have a spring shoot out at one point. When I bent down to pick it up I also found an extractor spring I had lost months ago and given up on.
Easier than making a ham sammich. Did my first one this weekend and it took about 20 mins. Put some tape over the receiver to protect it from scratching.