Oh, they're pretty long. In DC there's 5 towns you have to build up, 6 dungeons you have to go through, as well as a bonus dungeon. It doesn't sound very much, but it takes much time to through each of these towns and dungeons. I'm pretty bad with estimating hours, but maybe 40 hours or so? I don't know.

I'm not even half way on DC2, so I wouldn't know that, but I think it's longer than DC1. With sidequests it'll definitely be longer.