With four of you, you could indeed book Kevin's boat, Underwater Explorers, in Boynton Beach. I and many others are a big fan of his, and, more to the point, he is a six pack and the four of you would control the trip. That way, you could set your own departure time. This actually might be your best option for a couple of reasons.
The Castor, a wreck off of Boynton, is one of the best wreck dives around the entire area and in fact is my personal favorite. It is big, high profile, and covered in colorful sponges and orange cup corals. Don't forget your dive lights (you will need them at the bridge, as well). Even better, in September the Castor will be packed with Goliath grouper in their annual spawning aggregation. You might see 30 to 70 600 pound fish surrounded by swirling bait balls--one of the best "big animal" dives anywhere on earth, seriously. Boynton also has fantastic reefs, for the second dive. However, if you control the trip, Kevin might be willing to do only one dive. However, I really recommend a second, leisurely dive on a shallow reef, as the reefs at Boynton are great and you will not save too many $$ by cutting the charter to one dive--take advantage while you are here!
For me, a two-tanker, one on the Castor for big animals and one on a reef for corals and all sorts of tropicals, and then a dive later at the bridge for oddball macro critters, would pretty much meet my definition of a perfect day of diving. I am talking myself in to going along!!
The castor is an advanced dive, with the bottom at 110 and sometimes strong current to contend with, but from the number of dives I see in your post should not be an issue. Just wanted to let you know. You will want 34% and to rent a steel 100 if possible to max your bottom time. Kevin can get those for you. By the way, you might not spend hardly any time at 110, as the best parts of the wreck are from 75 to 90 feet and its more enjoyable to extend your dive by staying at those levels.
The schedule would be easy with a 9:00 am arrival. From FLL allow an hour to Boynton. So, say a departure with Underwater Explorers at 11:00. Return by 3:00. Boynton is only a half hour from the bridge. Load up and be at a shop near the bridge by 4:00, get tank,s and you are good to go for a 5:00 or 5:30 splash with plenty of time to eat in between.
If for some reason Underwater Explorers cannot do the trip (I would call them now to book as September is very busy due to Goliath season), you can also contact Splashdown Divers, another operator we really like and use all the time. Her boat is bigger, though, (she runs 12 divers) and you need to see if she will run with 4 people and let you set the departure time. She very well might do that so by all means contact her. My wife and I might even go as well to get her six, and I know she will go with 6.
