I suspect you've not gotten much for replies because diving there on such a short layover doesn't really seem practical, even if you can technically squeeze in dives with enough surface time. (Right after landing...after you get off the plane, and get through the airport, and pickup the car, and get...where?)
I like diving in Curacao, much prefer it to Bonaire. But on a short layover like that I personally wouldn't mess with diving, not to mention getting everything wet unless you're renting. I'd stick with getting a car and sightseeing, there's lots to see and plenty of good restaurants (all of which has been covered on other threads.) If you wanted to mostly check out the shopping, museums, and the many sights downtown, you could just stay in a hotel downtown and walk to many things. Maybe the Renaissance if you want a resorty environment, or the Dive Lodge (I don't know if they actually have diving at the site of the Lodge or anything that would work for you.) Or lots of choices depending what you want. Or you could stay in a hotel in the Piscadera Bay area which is still convenient to town and if you're less into cities and more into heading out to see the scenery. There's a Marriott Beach resort there which just reopened after renovations, and some others - also a couple dive shops nearby. (AFAIK no shop on Marriott property anymore, which is a shame because they reputedly had a decent shore dive from the old shop there and it might have worked )
That said, I expect you'd not make any morning dive boats so you'd be talking shore diving. (You with someone or need a buddy too?) There's dive shops right at some beaches and some lodgings with house reefs, but It's not a lot of time to get the lay of the land and get to the better shore diving sites, most of which will be more along the western part of the island. You could maybe stay at Lions Dive (east of town) for the night and just shore dive there, though not my favorite spot for shore diving. Or look up the Dive Bus which does shore diving in various locations, and see if they can work with your schedule. Or maybe Relaxed Guided Dives could work with you.