Most times I've been bar once (which was mid March) it's been November ish which is a nice time to go and I believe it gets hotter come mid to late April but still pleasant. It's worth bearing in mind that this is school holiday terms too so worth going a little beforehand?

I have always loved Hong Kong but it's been a few years since I've been there. I did do a Trip Report as below and I would definitely recommend, in no particular order. Lantua Island, Cheung Cheu and a Bus Tour of the mainland, Harbour Tour. The Peak as the basics. There's plenty of info out there but here's a snippet of my own little adventures.

BA A380 to HKG in PE/Y, IB Y/BA CE, Cheung Chau, MAD IB/CX Lounges and.... an FT Do!