Hi Keith-
You've provided some reaffirming insight. I did see that to visit Lunenberg and PC, it would eat up 7 hrs, leaving just about an hour or so for the Maritime Museum, which is also on my list. Being that it's summer, I would imagine these two locations are very busy.
So perhaps the half-day Historical Tour of Halifax would be worthwhile, as it visits the Gardens, Citadel Hill, Clock Tower, and several other sites, plus lunch in Dartmouth at Evan's. The tour owner appears to be well established and positive reviews. Plus there would be time to visit the Maritime Museum and dinner.