Thank you very much for your valuable and detail advice.
I need go out to work and let 99 to take care of bb. My reasons to send bb to nursery are that I want my bb learn independent (eg eat herself), learn "social", play and learn with other bb. Also, my bb is 活潑好動 and often 爬上爬落 (it seems that she is full of energy; is boring with all her toys and nothing for her to play). Going to school seems fit her needs. I also afraid that 99 will "chung" BB and only know taking care of BB but not frequently play with bb and bring BB to playground to play.
I really don't know which day BB will afternoon sleep as she sometimes don't afternoon sleep recently. As you said, only half-day school or playgroup may suit her much.
I know one playgroup held by a kindergarten but I need to go there by van. It's Mon-Fri 1:30-3:30 pm. In this 1-2 hrs parent/99 don't know go to where and seems 辛苦.
Do you think it is much better that I send bb to half-day nursery or playgroup when 2 yrs old and then to full-day kindergarten (the kindergarten I like) when 3 to let bb to learn independent?
I will try to find out some good playgroup or let my bb to join 1/2 day nursery near my home when BB is 2 yrs old. When she reaches 3, I will consider send her to kindergarten with half day / full time depending on her sleeping habit at that time.