We did a private excursion to Irie Blue Hole, aka Secret Falls through Liberty Tours. Note that none of the cruise lines offer this excursion, which I think is great.
Our guide met us at the the port then took us on an approximately 45 minute drive pointing out areas of interest along the way. When we arrived at the location, we were assisted by lifeguards who helped us down to the falls and took pictures of us with our cameras during our time there, approximately two hours.
The area was beautiful and secluded! There were a couple of other groups there as well, but nowhere near the crowds we've seen at Dunns River Falls. We had an awesome time jumping from the rope swing, swimming in the cool water and just hanging out in paradise.
After our time at the falls, our guide took us to Scotchies for some authentic jerk chicken and pork, rum punch for the adults! After lunch we headed back, stopping along the way for photo ops. We arrived back in Falmouth and had plenty of time for shopping.
Whatever you decide, I highly recommend a private excursion. The tour companies are very cognizant of the time, they don't want you the miss the ship any more than you do. Their tour business is how they put food on the table so the last thing they want are negative reviews on the internet due to not getting their group back in time. They offer a personalized experience that just can't be duplicated by the cruise lines. We walked right past all the huge groups waiting in the heat for their cruise excursion directly to our air conditioned private vehicle and were on our way to start our day.
If you would like more info, feel free to PM me.