I went to Florida for 2 weeks in February about 5 years ago and Presidents day fell while we were away.
While the parks were fairly quiet most of the time it was jammed packed on Presidents day.
I cannot remember how it affected the rest of the week but dont let it put you off because generally February is a great time to go to Florida as the weather is good but the crowds are fairly low.
We had weather into the 80s while we were there.
Maybe plan a non-park day on Presidents day, but the rest of the time it will probably be fine.