How to ask a potential postdoc supervisor to give me the postdoc interview results sooner than he planned
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.