16-20 is perfect for me....last time I went is around this weather. Its good because you'll be doing a lot of walking in HK and with that weather....you won't sweat.
The weather forecast is pretty accurate. Just wear a thick long sleeve jacket and you should be alright.

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Added on December 21, 2009, 4:04 pmIt's probably not such a good idea to book that early. Sometimes you get better deals closer to the date but not too close. I would recommend Bridal Tea House in Yau Ma Tei too, very small rooms but clean and conveniently located (just beside Yau Ma Tei MTR). ~450HKD/night during promotions. If you're on a budget, you can go for the branch in Hung Hom, HKD299/night but slightly further away from MTR and have to do more walking.

This post has been edited by eXTaTine: Dec 21 2009, 04:04 PM

If not mistaken, for Malaysians, should be able to get 5-day Shenzhen-only Visa-On-Arrival if you arrive by MTR at the Lo Wu station.