I'm from that area. Diving is further off shore 12-28 miles off shore & deeper, 65+ feet deep. There are some nice dives there, lots a spear fishing because the density of fish is enough to block the light.
Check with some of the local shops for available charters (its been 10 yrs since I was part of an op in that area). I think Dive Source in St. Augustine & Atlantic Pro Dive are running dive boats. Dive sorts include reef balls, barges, some wrecks, & the A6 planes ( pretty far off shore).
More predictable is cave country for some beautiful springs & caverns. Blue Grotto, Devils Den, Ginnie Springs, Akexander Springs, or Rainbow River.
It's worth the drive over to Crystal River area to see manatees while the water is still chilly.
So many options...so few days. Have fun!