Correct me if I’m wrong, but Spanish are not bottlenecked by their dock build speed. They need to build the TC build and collect wood before queueing their first fishing ship, just like any civ except Malians and Persians. The faster dock building speed only lets the vill that worked on it collect a bit more shore fish early on.
If that’s right, then activating Spanish bonus after the 1st TC goes up, much like Sicilians, isn’t that much different from only excluding their first TC but not the dock (or house).