My dreads were done by Trisha Star (the hairmistress of Chicago) and it took ten hours to complete. By the time Trish was done, I had 74 long dread extensions and a happy smile on my face.
Trish's prices are great as well-instead of charging by the hour (which can get VERY costly), she charges per dread. Although it cost $300 dollars to get my hair dreaded, it was worth every penny. So far I have had the dreads in for a month and most seem to still be securely attached to my head. Although some dreads on the lower portion of my head fell out, I expected them to because the hair there was rather short. I suspect that the rest of the dreads will stay in my hair for about another month and a half.
One downside to having the dreads done this way is that my natural hair sometimes "flys away" from the extensions because of its length. I sometimes try to weigh my real hair down with wax, but unfortunately, little portions of my natural hair always manage to stick out. The only other downside is that my scalp gets EXTREMELY itchy from having these in, but in the long run it's totally worth it. You have to suffer to be fabulous sometimes, after all :)