There are some decent ways to incorporate tech diving on a recreational Caribbean style charter ... but it really depends on the staff, the tech divers, and the topology of the area ...
One shop I dive with, we will splash during the dive briefing, sometimes we need to swim aways to get to the site (depending on area and surface conditions .... briefing and then subsequently gearing up 14-20 rec divers in swells for 20-30min wouldn't be a good option), Others, we get dropped off on the way to the area where they do the briefing ..
This gives us a good 25-30min head start from the first recreational diver splashing .... Depending on the site and equipment we are bringing, we try to get on the boat before the divers get back, so we get a 90-110minute run time on the first dive (especially when bringing DPV, stages, etc ... easier to stow away without people in the way on deck)
Second dive is very similar, splash just before the briefing (grabbing equipment when most people are out on the fly bridge/bow sunning while on their SI)
We will generally get out of the water last on the second dive, getting in another 90-110min dive, as most of the rec divers are now tired, and not hanging out around the back of the boat while the crew strips down the gear and starts rinsing the equipment on the way back to the dock.
While not a good 3-4hr CCR dive, with OC/CCR tech divers it works out fairly well.
_R