I had heard comments about this excursion being boring so hadn't suggested it on our cruise. Mom and Aunt (80 somethings) found it in the Navigators and booked it on the island. I think they went ashore first thing and did the first trip of the morning. I know they were through by 11:00 or so when we ran into them on the island.
They said they really enjoyed the trip and felt it was well worth the money. They mentioned seeing the coral formations and lots of different fish. Neither one mentioned it being rough and Mom had some problems with a queasy stomach earlier in the cruise so I'm sure she would have mentioned it.
I think it really depends on the age and expectations.
As to the best time to go, depending on the time of year, it might be much warmer later in the day. Also, when we were on CC it was windier in the afternoon than in the morning.