Actually, I think your Feb. dates look great! They are not President's Day weekend, as that is the weekend prior (2/15-2/18). The problem with your March dates is that they are very close (if not bang on) Spring break. The first week of April is traditonally the pinnacle of spring break, but the week or two prior or after that is still bad.
I went in Feb. (around the 11th) last year, and it was SO not crowded. I have been to DL 2-3 times a year for the last 12 years or so, and that was my first Feb. visit, and it was so empty I almost couldn't believe it. So, I am sold on Feb. I can see how President's Day weekend would be not so good, but you are not planning on going then, so I would say your new dates look great!