We are at OKW from 21st Jan, And we were there the same time this year.
This year is the hottests its been in Jan for a few years, we always go this time of year, but have also been in October and December.
It was high 70's low 80's this year which we werent really preparred for. lol. I would reiterate what others have said, plan for both. Def need a jumper, even a coat on some nights. Was essential for us on the boats to DTD at night - not exactly open water, but it def makes a hell of difference when you pull into the lagoon area of DTD.