Your eligibility under review may result in some additional necessary processing time. But don't worry, it doesn't mean something is wrong with your application. Some agents put a file under review if they can't understand a little detail. So instead of taking a risk, they prefer to leave it for someone else to judge.
Impossible to say when exactly PPR should come, but sometimes processing times goes a bit over 6 months without making it abnormal (like 6.5 months).
If you want more details about your application processing, order GCMS, and you'll probably know exactly why your eligibility is put under review required.