You count such a watch by the time he starts his class.

　　你總是掐著他開始上課的時間。

　　Most of the workers had already rung in by the time I arrived.

　　我到的時候，大多數工人都已簽到了。

　　By the time she left college, she had been an excellent student.

　　到她大學畢業的時候，她已經是一個優秀的學生了。