It will be February. Even if it's Florida, it will still be cold-ish. Orlando's average February low is 52. The sun won't be out. There have been years when we've gone down into the 20's at night. I don't think you'll want your belly exposed.
Actually, while last year was chilly b/c it was overcast and rainy, I still was pretty warm once I started running. I was wearing a running skirt and a ss top and was comfy. The year before that was HOT once the sun came out. I was in Corral B and the sun came up right as I was going through the MK. After that, the whole second half of the race was sunny and hot. So it's a mixed bag, for sure. Even last year on Saturday when we toured the parks I was in a tank top and shorts. The very next day (race day) I was wearing jeans, a ls tee and had a light jacket when it got breezy post-race. So, basically, have outfit plans A & B ready!