When does evening, 晚上， begin in China? This is from a little text about 俞伯牙弹琴。 Travelling on a boat, they stop to wait for the wind and waves to calm down.

晚上，风浪渐渐平息，天气晴朗，江水清澈，景色十分迷人。 望着空中的明月，俞伯牙来了兴致，拿出琴弹了起来，一会儿他酒沉醉在了音乐之中。

zdic.net: 晴朗： 阳光充足,没有云雾

晴朗： sunny, fine and cloudless

He gazed at the bright moon on this evening and played his zither. 
(Reminds me of Alice Through the Looking Glass: "The moon was shining sulkily, because she thought the sun, had got no business to be there, after the day was done.")

Even in ancient China, the sun did not shine at night, did it??
well, you're reading a bad example of written vernacular chinese, trying to pretend it has a classical chinese origin, with invented details.


  天氣晴朗


it's an error. the possible choice of word is 清朗 or 澄朗; both means clear, crisp sky.

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?o=dcbdic&amp;searchid=Z00000102154

about the starting time of evening, in ancient; it's 1900 hrs.

one night (一夜) is divided into 5 night-watches (五更); midnight is 三更, 

戌時 (1900 - 2100 hrs) is 一更

子時 (2300 - 0100 hrs) is 三更, that's why we've "三更半夜"

http://dict.revised.moe.edu.tw/cgi-bin/cbdic/gsweb.cgi?o=dcbdic&amp;searchid=Z00000144495