After having asked around in forums and WhatsApp groups I've come to the conclusion that no one seems to know the exact answer to this. Some people have said that thir employment letters did not mention how many h a week you work and they got PPR. Others say that they know of cases were the app has been rejected due to this.
So my plan is to starting from next week, to contact all my employers and ask for a new letter only with this info in it. And then raise a CSR through the CIC webform just to be on the safe side. Coz it would be so lame if this would be the only reason I got rejected.
So if you are in the same seat as I am, my suggestion would be to try to get new letter.