You have to go around to the Kng. side to hike to the peak. Most visitors spend the night at the hostel, then hike in the dark to the peak in order to see the sunrise (if it's not cloudy.) I preferred to hike during daylight and, with friends who had a car, left Port Antonio about 3:30 am, drove to Kng. and then up to Hagley Gap where we left the car, took the Landrover to the trail's start and began hiking about 9/9:30 am. With just 2 of us and Albert Harley, out of Ivanhoe Guest House, as our guide, we reached the peak around noon. --- in sunshine!
We returned to Port A. that night. While you can't reach the peak from Portland ( well, you can but it takes a few days and a really good guide and overnight camping etc.etc...) Albert offers some really good day hikes around Portland in the John Crow Mtns. which are the foothills of the Blue Mtns.
Be warned that, in and around Port Antonio and Portland, everyone and their brother will offer to guide you to the peak or to hike in the Blue Mtns. I recommend going with Albert Harley or someone he recommends. Do NOT go with the guys at the green house on Titchfield at the corner of Musgrave and Queen St. nor with "Garfield" who may be at Ocean Crest.
A note: Bring food if you hike to the peak. You'll be starving when you reach it.