What's the difference between "what time"and"when"?what time 和 when 在用法上有什么不同?

一个是问具体时间啊，一个是问大概时间。

what time常用来问钟点，而when除了问钟点外，还可用来问日期，月份，年份等。有时两者可以换用，有的场合不可以。
1.问钟点时，可以换用。
When do you go to school?
What time do you go to school?
2.问日期，月份，年份等，只能用when
When were you born? I was born on July 2,1972.
3,当问某事在某天的什么具体时间进行，只能用what time
What time did you call this afternoon?
I called at 4:00 this afternoon.
另注:
when :
一,副词 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.
When did you last see Margaret?
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.
二,连接词 conj.
1.当...时
John got engaged to her when travelling last winter.
Don't get excited when you talk.
2.既然,考虑到
How can he get the promotion when his boss dislikes him?
3.虽然,然而
I had only fifteen dollars on me when the book I wanted cost twenty.
4.在那时,然后
三,代词 pron.
1.什么时候,那时
Since when has she taught here?
四,名词 n.
1.(事件发生的)时间[the S]
what time:
什么时间 问具体时间，如几点钟
例: What time is it now?
What time is suitable for us to meet?
望楼主采纳。

what time是提问几点几分,精确的时间
when是提问何时,大概的时间
例如：
What time does he come back?At six thirty.
When does he come back?In the evening.