having done 放在句首:when的用法

具体你可以参考这一段。
when，while，as引导时间状语从句的区别
when，while，as显然都可以引导时间状语从句，但用法区别非常大。
一、when可以和延续性动词连用，也可以和短暂性动词连用；而while和as只能和延续性动词连用。
① Why do you want a new job when youve got such a good one already？（get为短暂性动词）你已经找到如此好的工作，为何还想再找新的？
②Sorry，I was out when you called me．（call为短暂性动词）对不起，你打电话时我刚好外出了。
③Strike while the iron is hot．（is为延续性动词，表示一种持续的状态）趁热打铁。
④ The students took notes as they listened．（listen为延续性动词）学生们边听课边做笔记。
二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生；while和as从句的谓语动作必须是和主句谓语动作同时发生。
1．从句动作在主句动作前发生，只用 when。
①When he had finished his homework，he took a short rest．（finished先发生）当他完成作业后，他休息了一会儿。
②When I got to the airport，the guests had left．（got to后发生）当我赶到飞机场时，客人们已经离开了。
2．从句动作和主句动作同时发生，且从句动作为延续性动词时，when，while，as都可使用。
①When ／While ／As we were dancing，a stranger came in．（dance为延续性动词）当我们跳舞时，一位陌生人走了进来。
②When ／While ／As she was making a phonecall，I was writing a letter．（make为延续性动词）当她在打电话时，我正在写信。
3．当主句、从句动作同时进行，从句动作的时间概念淡化，而主要表示主句动作发生的背景或条件时，只能用 as。这时，as常表示“随着……”；“一边……，一边……”之意。
① As the time went on，the weather got worse．（as表示“随着……”之意）
② The atmosphere gets thinner and thinner as the height increases．随着高度的增加，大气越来越稀薄。
③As years go by，China is getting stronger and richer．随着时间一年一年过去，中国变得越来越富强了。
④The little girls sang as they went．小姑娘们一边走，一边唱。
⑤The sad mother sat on the roadside，shouting as she was crying．伤心的妈妈坐在路边，边哭边叫。
4．在将来时从句中，常用when，且从句须用一般时代替将来时。
①You shall borrow the book when I have finished reading it．在我读完这本书后，你可以借阅。
②When the manager comes here for a visit next week，Ill talk with him about this．下周，经理来这参观时，我会和他谈谈此事。
三、when用于表示“一……就……”的句型中（指过去的事情）。
sb．had hardly（＝scarcely） done sth．when．．．＝Hardly ／ Scarcely had sb．done sth．when．．．
①I had hardly ／scarcely closed my eyes when someone knocked at the door．＝Hardly ／ Scarcely had I closed my eyes when someone knocked at the door．我刚一闭上眼，就有人在敲门了。
②I had hardly ／scarcely entered my room when the telephone rang．＝Hardly ／Scarcely had I entered my room when the telephone rang．我刚一走进房门，电话就响了。

When(当....的时候)

1.When I grow up,I want to be a teacher.
当我长大的时候,我想成为一位老师

2.Please tell me when he comes back.
当他回来的时候,请你告诉我

when也可以作提问,例如:

When will you arrive?
你什么时候到?

When和what time差不多,都是问时间
但 what time是问具体时间,例如:
what time is it now?
现在几点种?
when是问较大的时间段
when were you born?
你什么时候出生?

KK: [ ]
DJ: [ ]
ad.
1. (用作疑问副词)什么时候,何时
I'd like to know when they'll let him out.
我想知道他们什么时候放他。
When did you last see Margaret?
你上一次见到玛格丽特是什么时候?
2. (用作关系副词,引导关系从句)当...时
There were times when I didn't know what to do.
有些时候我不知道该怎么办才好。
conj.
1. 当...时
John got engaged to her when travelling last winter.
去年冬天旅行时,约翰与她订了婚。
Don't get excited when you talk.
你说话时别激动。
2. 既然,考虑到
How can he get the promotion when his boss dislikes him?
既然上司不喜欢他,那他怎么会获得提升呢?
3. 虽然,然而
I had only fifteen dollars on me when the book I wanted cost twenty.
我身上只带了十五美元,可是我想买的那本书定价二十美元。
4. 在那时,然后
pron.
1. 什么时候,那时
Since when has she taught here?
她从什么时候开始在这儿教书的?
n.
1. (事件发生的)时间[the S]

when 疑问副词 什么时候

when do you get up every day?
你每天什么时候起床

这句中的when可以替换为what time
what time do you get up every day?

when 还可以用来表示:虽然,然而,可是等意思,例如:
He usually walks when he might ride .虽然有车可坐，他通常总是步行．
when 还有”既然，考虑到”等意思：
How could you, when you knew that this might damage the apparatus?既然你知道这会损坏仪器，你怎么能这么做呢？

深奥