the time during whichThe time when I first met him was a very difficult period of my lifewhen为什么可以改为during which还有百度上说的during which 和during which time的区别按照：看前面修饰的名词是指具体的时间还是一个含有时间概念的名词,如果是具体时间,则用during which time；如果是后者则用during which

the time during which
The time when I first met him was a very difficult period of my life
when为什么可以改为during which
还有百度上说的during which 和during which time的区别按照：看前面修饰的名词是指具体的时间还是一个含有时间概念的名词,如果是具体时间,则用during which time；如果是后者则用during which