The correct time to use is 10:10 although many people break this rule. I look at it like the rule of thirds, most of the time it is better to use the rule unless you have a specific reason to break it.
Next, look at a lot of watch photography, I would suggest
www.timezone.com for lots of examples (good and bad) as well as what people want to see in their watches. Use a soft box and limit reflections as much as possible (I like to use a dark room, everything in front of the watch black, the rest lit by continuous lights so I can see all the reflections and get rid of them).
My last tidbit is that if you are photographing high end watches commercially you will need awesome sharpness and detail. Either the best DSLR and lens on the market and awesome photoshop skills, or medium format digital, or large format film. The market is cutthroat and some of these companies pay big bucks for the ultimate in advertising images. We aren't talking people spending $350 at some mall jewelery store, we are talking $3,000 to $300,000 per watch. People spending that kind of money will not accept any, and I mean any, flaw.
When I bought my GP, one speck of dust under the crystal visible with a loupe would have caused me to not purchase it. For that amount of money, it had to be flawless.
Allan