Hey, Dave, as long as you can take a day off YES, I would make time for the Keys. It's just the best diving in the US... well, I grew up in CA and think it's better here anyway. Everybody has an opinion!
You'll need a whole day. AM dives are almost ALWAYS better conditions than PM dives. It's nice to stay down there the night before, and get up and dive the next morning, but I often drive down EARLY from Lauderdale by the Sea rather than stay. You'll be leaving about 3:30 AM and it's a long drive. There are good operators beginning around mile marker 100, I think. Now, if you drive down early and do a couple of deep dives, I warn you that the drive home will be HELL unless you're a long-haul truck driver or something.
Dives are double-dips... usually a wreck and a reef. Most operators check credentials for deeper dives (spiegel grove, duaine, etc.), so see what their requirements are before you book. They're all good as far as we know... there haven't been any threads bashing Keys dive ops, anyway.
Since you won't be back, I'll suggest you do a double-double dip... that's an AM and PM boat - four dives! A couple thoughts: this will probably wear you out. I actually fell asleep on the highway on the road back... didn't even know it was happening until I heard the thump-thump-thump between lanes. I'll *never* do that again without getting a hotel. I do a lot of long drives and I've never fallen asleep before like that.
Anyway, don't miss the restaurants either way - make time for one or two. Little local places are tucked away off the beten path all over, and the Keys has attracted some award-winning chefs. Prices are usually reasonable and each dive operator has a little cluster in their area, so talk to them about it OR after you've picked an operator post here.
PBC has great diving, but if I had the time I'd do the keys for sure! Have a blast here either way!