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Would you mind telling me how many days does it take for an author to get feedback of whether the article is rejected or approved?

There's no definite answer other than "it depends." It depends on how busy the review team is, how many articles are in line in front of yours, how many public and private requests are active, and so on. . . A week wait for any of us, new or established, isn't unusual for non-requested articles. That said, you won't have to wait months to hear back as with some traditional publications.