How to ask a potential postdoc supervisor to give me the postdoc interview results sooner than he planned 25 Mar 2018
I had a Skype interviewer with a potential postdoc supervisor, and he mentioned that those who passed the first Skype interview will be informed after he interviews all people, which is around 2 weeks prior to a second formal interview held at his institute. 

I am in another country and will need 2-3 weeks to apply for a visa to go abroad for the second interview. If I am told the results after he finishes interviewing all people, I am very likely not able to obtain a visa in time for the scheduled second interview. 

Could you please give me suggestions on how to write to him about this situation without being rude. Thank you very much!

----20 June 2018
Sevel months have passed! How time flies.
To follow up, I didn't ask him to give the results sooner than he planned.
And I didn't get the job either.

That was my first skype interview, so I didn't have much experience and failed it.
But now, I have received a great offer.
Rather than asking to know the results in advance, which may not even be possible (they probably tell you the results as soon as they have reached a decision, and they probably cannot reach a final decision without interviewing everyone), ask if it would be possible to delay the formal interview if you do get to that stage. From what you've told, this would mean one or two weeks of delay at most; that's nothing. Explain your situation with the visa and I'm sure anyone reasonable will understand.