About 11 pm

Yes!! But it will be crowded!!

I think the street may be quiet as Monday Tuesday most businesses are close for rest days. Fyi.

Partially open as many of the Chinese vendors celebrate christmas here, so they are not supposed to open the shops that day. Better you go and check it out as it is very near to other attractions like Church Square and you have to just walk around to reach the place.

I am not sure

Better ask the shop before buying to be sure. It usually varies from one shop to another.

I guess it opens fri-sun nite. Other nights not so lively as weekend but many stores open though

I visited last week during the long weekend (where the Friday it was a national holiday for Singapore and the rest of the weekend as well as Monday was a religious holiday in Malaysia). Each of those days of the weekend the market was open (as of 5pm until past midnight). Plus it was very crowded due the holidays I listed. I recommend not to visit during a holiday but if you are worried whether it will be open or not I'm pretty sure it will be.

Shops are open for daytime business. But nighttime bazaar is open only on weekends. I guess you could give it a miss if you intended to be there on weekday nights.