Really, really (since you've obviously never been to HK before) - don't even think about doing this behind glass. For sunrise / sunset shots you need clear views east and west. From one hotel room that's pretty unlikely. There are any number of excellent vantage points around HK which are far better than hotels.

Up on Luggard Road (round The Peak) is an obvious vantage point. But you could also jump in a cab to the top on Tai Mo Shan (the highest point in HK - over 3000') and try from there.

For sunset over HK Harbour you need to be up on somewhere like Devil's Peak, or perhaps lower down on the waterfront at Lei Yue Mun. For sunrise over the harbour on a clear day then maybe the pavillion at the top of the hill on Peng Chau?