Actually, looks like you're going to be in the dark the whole time. Take a look at the sun/moon schedule at SunriseSunset.com.Looks like we'll be loosing the moonlight during our stay (2/14/09-2/21/09).
On Saturday, sunset is 6:39pm, with twilight at 7:00pm. The moon (waning gibbous, almost to first quarter) doesn't rise until 11:19pm, four hours and forty minutes after sunset. The following night, it's after midnight before it rises, and so on.
You could get in some nice daybreak dives (like night dives, but you start early morning and let the water get brighter and brighter), but that means getting up early. I did at least one night dive and a daybreak/dawn dive every day in Bonaire, but I wasn't planning to get any rest until I got back.
Of course, you don't get moonlight, but you'll get to have *very* black water. That is cool in a different way than moonlight dives (and when I keep saying dives, I also mean snorkels, of course), but it's quite amazingly cool, too. (It'll also make your lights seem all the brighter.)