Odd question, is it warmer the first week in January or the first week in February in Orlando? It sounds odd, but it is warmer where I am the first week of Janurary.:shrug:
The mean temperature isn't as good an indicator as it might sound. I find it often low by 5-10 degrees of a daytime high. You can expect it to be cooler in the evenings and night. Enough so to put on a light jacket. There is the occasional cold snap that can move through but not often.
I've been down in mid January where you could have been in the pool during the day, but that's not always the case. The weather tends to fluctuate at that time of year, so like was said above you can get cold or warm snaps, you never know.