We have been going to Disney in February for the last 6 years! This is the first we have missed in a long time! And it hurts!!! We def get to swim on the February trips. Night swimming is a little harder as the pools will open 10-ish in the morning and then close 9 or 10 depending on the resort. But it is usually warm enough during the day for swimming! We usually need light jackets for the AM and PMs but shed them once the sun comes out. We have had days where I wish I had packed our personal fans and cooling rags. And days where we needed jackets all day. It does vary a bit but I don't think we have had 1 Feb. trip where we couldn't swim at least some of the days.
We went to Disney last year right after Thanksgiving and MUCH cooler!!! But we enjoyed it. Our friends were a little disappointed at how cold it was. But the pools are heated and my crazy children don't care, they will swim no matter what.
We tend to go around President's Day, just to save on a school day missed. But it is busier that weekend, traditionally. If you can, I would go a week before or after President's Day weekend. There is a small sweet spot before spring breaks start. But overall February is a great time to go. It has gotten more and more popular time of year to go. But really who knows what it will be like going forward.
So, Christmas decorations will start to go up literally right after Halloween, but not all of the Christmas stuff will be up till closer to the end of November. The holiday booths have traditionally opened on Black Friday. So, depending on what holiday stuff you want to see, you will want to go later in November. If they have the storytellers this year, those also usually start Black Friday.