I did arange for day trip to Kingston from Negril one time to Japanese tourist customers.
It is possible if you know how to get around or know where you want to go in Kingston
You can get on Southcoast Express @4:30am and get to Kingston around 8:30am-9am.
I ask Kingston tourist guide to pick them up from kingston bus stop and take Bob Marley tour(Studio, memerial, and other spots) till 4pm.
Southcoast Express from Kingston leave @5pm and get back to Negril by 9pm.
It is possible... but I wouldn't try around election days(Dec 29th).
South Coast Express is 2200J for one way advance ticket. You can purchase at the counter by Hilow shopping plaza.
Some people go to work to Kingston with this bus and come back in same day.
Try and see how it goes
Good Luck
