Winderdawg

Edit: I see someone already answered your question. It has to do with flow through the narrows. If the flow is not going in your direction, they will not allow you to enter. We only found this out because there was a medical debarkation on our southbound trip and we missed the original window for us to enter the Seymour Narrows. The ship waited for our next window and were about 5 hours late arriving in Vancouver.

That isn't always the case. We were on the NCL Jewel 7/3/23 sailing and we sailed through the Seymour Narrows.

We did the precruise extension in 2015. It’s really more like one day on your own. The first day, we arrived mid afternoon and went to dinner and bed. The third day had our transfer to the ship early enough we had to cancel our planned morning excursion. We did a circle island tour with Pearl Harbor, but had very little time to do some of the other things we wanted to. If you’re wanting to see more of Oahu, I would extend post cruise or do your own pre cruise arrangements.