I sent my cv around 10am on Sat. 13 June 2020 to a PI for a postdoc position which was posted about a week ago.
He replied around 3pm on the same day and scheduled an interview for Friday 19 June. His email was extremely enthusiastic.

I cannot say how the interview went. Probably not perfect, but no big accident.
In the end of the interview, I thanked him, and he said: I will talk with people in my group and will get back to you next week.

On Monday morning, 22 June, I wrote a follow up letter, but at that time, I had some concerns about his idea, so the letter sounded too reserved. I read more and in the afternoon same day, I wrote another message with much more enthusiasm with explanation what concerns I had.

About the position: He is looking for wet lab postdoc with some experience in dry lab. I am dry lab with no experience in wet lab. I think he decided to recruit a dry lab after seeing my resume.
During the interview, I asked him some thing on the advertisement, and he said he has several openings.
He founded a small bio-tech company with some other professors. Currently, 2 of his postdocs are funded from the company.

My references told me that he contacted them before the interview.

So far, I no update from him. Since he has been very fast, arranged interview on the same day I applied, and it was Sat., I started to feel pessimistic, Things have been very difficult for me this year.

I had interviews, and will have more. But even if it is all up to me to choose, I think I would choose this job.
How much chance do I have for this position?

It sounds very promising and I wish you all the luck. However you won't know until they tell you and it it is still very early. Many HR policies must be considered when hiring and the job cannot be given until all the interviews are conducted. Also when applicants are being considered for multiple vacancies it makes decisions take even longer. While sounds like you aced the interview it would be unlikely to hear back this soon.