Not really enough to worry about in my opinion.
Check also the tides for Gold River and Zeballos - it is generally only a few minutes difference. Split the difference.
There is nowhere in Nootka Sound that I am aware of where there are heavy currents to contend with, and the difference in tide would be inches. Unless you are trying to squeak into a lagoon at high tide and need maximum depth, I can't see it being a factor.
As for fishing tides, it's nice to know when slack tides are so you can fish hard during those times, but what are you going to do, not fish until the perfect tide?
As for rocks and shallow spots - give them a wide bearth where ever possible, and be cautious when you can't.