Hi Brian,
That's 4 and a half hours from Lauderdale by the Sea.
It's about 200 miles and a lot of it on US 1 in the keys.
You won't make the 3 pm snorkel trip at Pennekamp and be home by 8 though. Do stop at Mrs Mac's on your way down.
Another half way stop is Lorelei across from Islander in Islamorada.
Cheers
irina