It can be somewhat normal, this does seem to happen sometimes to books, that they can take 4, 5, 7, 10 and even 14 days before being approved for whatever reason. This seems to be a random event, one week you could have a book approved in 10 days, and a week later the next book takes 3 days.
As of early summer 2024 it has been taking 7 to 10 days for a book to be approved, so you just have to be paitent with them and keep working on new books.
Best advice we can give, is email after 2 full weeks and ask them if there is a problem with the book that it has been in review for so many days.
They should respond within a few hours.
Check your KDP dashboard daily, make sure it is still in review or maybe it has been approved, the emails to be approved can come hour(s) after it actually happens. But mostly, if you see it has gone back to draft mode, then that means there was an issue with it, and they will send you a email, sometimes it will come a few hours after the book is kicked back to draft status. Be sure to check your junk mail folder as well.
Also if a book does get rejected, this is not something to leave for days or a week or two. They have been known to close accounts in some cases if the issue does not get fixed.