I've bought a few watches from Elegant Watch & Jewelry in Ocean Terminal. Very happy with them, but you must bargain wherever you go! Elegant also has other outlets in TST and on the Island.
In general, you can expect a maximum of about 40% off the list price on the watch (whatever brand). The best I have attained is 38% paying by cash rather than by CC (the salesgirl accompanied me to the ATM to do an online transfer to Elegant!).
Just sometimes they have specials (aaarrrgg, ...old model!) that they will sell for around 66% off the list price, which are fantastic bargains, but they obviously need to be what you want.
Shop around at other watch shops just a little to establish that the "List Price" is consistent for the model you are after and not inflated, before you negotiate towards the 40% discount.