Is there any difference between these sentences

[HerTz]

Could you please tell me the difference between these

When have you seen him?

When did you see him?

Also can I use before in the following sentence:
Have you seen him before?
I mean present perfect is used when there is no specific time, so is before counted as a time phrase.

 

[5jj]

Could you please tell me the difference between these

When have you seen him?

When have you seen him?

There is no difference, Indeed, they are identical.

 

[HerTz]

There is no difference, Indeed, they are identical.

I'm so sorry I fixed it.