Yes we did this a few years ago. Rented a car from near the station; drive to beyond Lunenberg so we could catch the ferry at LeHave - had lunch in Lunenberg, then to Mahone Bay, skipped PC, then to the Titanic. Dropped car off then went for a beer. Note: we did have a late departure from Halifax - around 9p I think so we were not rushed.
Next month we are planning on going straight to PC then back via the lighthouse coast route, to the Titanic but we have to be back on board by 4:30.
Car rented from Avis in Hollis St.
If you want to see Lunenberg then s4 of The Sinner starting Bill Pullman was shot there