We’ve been Jan. 7-15 in 2014 and 2015. I can’t stress enough that you should be prepared for warm and cold! Definitely check the Orlando forecast right before you go (I know that makes it hard to pack ahead of time). Generally, the temps are chilly in the morning (40’s-50’s), warm up during the day (70’s, maybe 80’s), then get chilly again in the evening. However, this year we had a morning of cold (30 degrees, with a wind chill in the 20s!!) and we were glad we had our mittens! I usually take mostly jeans and capris, and a few pairs of shorts. My DH likes the cool, so he tends to wear shorts more. You will likely need layers. We mostly wear short sleeve shirts, with sweatshirts or jackets. (Some mornings I wore a sweatshirt and a jacket😄) Then you can shed as you get warmer, and put back on when you get cold again. We saw several people who had no idea that it could get cold in FL. They were in the gift shop buying more clothes.
I hope you enjoy your day your trip. We really love going in January.