From my experience the delay from satellite TV and from streaming NowTV from my tablet cast to my main TV are both around 20 seconds. I know this from syncing up radio commentaries from DAB radio to TV sports coverage. OTOH streaming radio commentaries can be up to two minutes behind which makes them useless for watching sports on a noisy pub TV for example.
Certainly Sky Sports Main Event on BT TV does not present a significant delay. Compare the time on the screen with that of an online bookmaker (which has to be up to date) and they are almost identical.