Haven't watched this TV show, but it looks like it being aired weekly on Sky One, where the next episode 8 will be broadcasted live & exclusive on Sky One at 9pm tomorrow, then i would expect episode 8 to be added to NowTV Catch up.
Where Episode 9 will follow the same time the week after in 7 days time.
What you absolutely must bare in mind with Sky is that they will not pick up every TV show straight away.
This often happens with FBI, SWAT and Blacklist to name a few.
Most of the time Sky wait till the season is finished to start airing it here in the UK.
Only on Sky Atlantic will most shows be aired within the same week or month. Like Ray Donovan, Game of Thrones etc.
Some series, e.g. Little Birds, are released to catchup in their entirety as soon as Episode 1 is streamed.
Others are released only week by week, as each episode airs live. Prodigal Son is one of these.
I do not know what determines the difference, whether it is rights issues, maximising the live audience, or what, I am afraid.