Maybe a late start, it would need to be quite a short route to get back for 09:55.
I've noticed though that the Poznan services are also not timed right.
Tuesday
FR3949 07:40 Poznan
FR3948 12:35 Poznan
Saturday
FR3949 08:45 Poznan
FR3948 15:25 Poznan
The return service on Saturdays is far too late. That flight (FR3948) on Saturdays leaves Poznan at 12:25 local time. As the UK is one hour behind Poland, that would mean it takes 4 hours to get back
As all other flights on this route are scheduled as 2hrs 15mins, this flight should in theory arrive at 13:40. That would also make sense as a flight to Dublin leaves at 14:30 and the usual turnaround time is 50 minutes when they do a crew change.
I don't know whether it's a mistake or wheather they can't get a slot around that time as between about 1 and 3 on a Saturday afternoon is packed full of the holidays flights by Jet2, Monarch, Thomson etc.