I started it on a Friday evening and had it finished on Sunday (except of course the buttons). I had a lot of knitting time that weekend though, so if I were going to add up the hours, I'd estimate about 10 or 12 hours of actual knitting time. The cabling definitely slowed things down, but I found that once I got the pattern established, I could glance at the chart and compare to my knitting to see which type of cable came next, without having to really look at the key, which helped me to stay in somewhat of a rhythm.
By the way--I used Amy's video for the one row buttonhole for this project and it worked great. If you haven't tried that type of buttonhole before, you might try it out.