Am Sabahan, from KK.
Like most of those who have been there, there are 2 ways to go up to the summit. i.e old trail and the new trail (Mersilau). Old trail is shorter as compare to the new trail.
My bro. has 2 times experiences with Mersilau but me none. By the way, we have been up there every year during our sec. & high school holiday. So his comment was Mersilau has more flora.
My experiences will only be on the old trail.
You can drive / take bus, taxi, tumpang.... to the Mt. Kinabalu national park at anytime. The climbing HQ is next to the park entrance. All payment is to be made by cash and on the spot. The locals are hired as a guide and your porter. Carrying your stuff cost RM7 per kg but minimum charge is RM70.
The guide basically just to assist / keep an eye on you in case you need help (not really proper medic trained). They will wait for you along the journey.
About this period, I am not too sure about the weather. The best is you are only sweat when you reach the rest house (before the summit) instead wet by rain. It would be very cold if you don't dry clothes for change. Food selling at the rest house is about RM15 per item.... even hot water cost $$$. For sure, a rain coat (for yourself) and plastic bags (for your clothes, items, cameras...) are must. Very rare chances that climbers did not experience rain.
You will rest (here or other huts) like others mentioned and continue the journey in the early 3 a.m. to reach Low's Peak catching the sunrise. This is the time either you use a torch (no moon) or no torch (full moon). It's beautiful looking down the villages / town faraway and the clouds beneath your feet at night....
After enough of wind blow, photographing on summit, you will return to the rest house and pack up to return to your starting point.
The distance: HQ to starting point (3.5km) by park's bus. Starting point to rest house (6 km). Rest house to Low's peak (3 km).
Normal walk distance: 1st day (6 km), from starting point to resthouse.
3am onwards (12 km), from resthouse to summit, summit to resthouse, resthouse to starting point.
Please note that you have to book a bed at the resthouse in order allow for the climb. else you can't go up.
Hope this general guide helps. You can do the booking online http://www.suterasanctuarylodges.com.my/