I've done Glistening Waters/Luminous Lagoon several times and put together a day trip for friends that included a visit. It is really cool and I highly recommend it. From Negril it makes for a late night as it's 2 hours away and an after dark kinda thing. We always stopped on the way back to Negril from Ocho Rios. You can have dinner there and take a later boat for optimum dark. There is a lot to do on the north coast to put together a variety of day trip fun. Rocklands Bird Sanctuary in the hills above MoBay. The actual city of Falmouth as a opposed to the Cruise port theme park version. Discovery Bay historical park, where Columbus landed, and they have a Scotchies there now for good jerk. The Marley pilgrimage to Nine Mile in the hills of St. Ann, the drive alone is a spiritual experience. There's everything from alligator farms and Arawak caves to Dunn's River Falls and Mystic Mountain. Make it an adventure!