I agree with Murph's and bnewb's recommendation to scratch Dunn's River Falls.

Dunn's River Falls is located in Ocho Rios which would be a very long road trip from Negril. It can be done, but I would suggest you spend the time exploring around Negril.

Of the three major falls I've been to in Jamaica, Dunn's River is my least favorite. The cruise ships that dock in Ocho Rios send too many tourist to Dunn's River. If you get real lucky and visit on a day when no ships are in port it is okay, but that doesn't happen too often.

Mayfield Falls is a 1/2 day trip from Negril. Y&S Falls can be combined with several other options like Appleton Rum Tour, Black River or Pelican Bar for a very nice day tour from Negril.

Enjoy,

VVHT