Reviews will generally show up within 72 hours of posting.
With that said, students at Self-Publishing School have had different experiences with review posts being delayed.
Some reviews have been posted immediately, which is great!
Some reviews take a little longer to be posted, sometimes up to 4 or 5 days.
It's completely up to Amazon on how long (or even if) a review will be posted so if you're having difficulty seeing reviews, please reach out to Amazon directly.
It's always a good idea to ask your launch team to tell you when they've left a review so you can keep an eye out for it. Be sure to thank them for leaving a review!