ELI5: Why is it recommended to sleep 8 hours when a sleep cycle is 90 minutes so it should be 7.5 or 9 hours? Won’t you wake up mid sleep cycle (and be groggy) if you set your alarm for 8 hours?

ELI5: Why is it recommended to sleep 8 hours when a sleep cycle is 90 minutes so it should be 7.5 or 9 hours? Won’t you wake up mid sleep cycle (and be groggy) if you set your alarm for 8 hours?