Make a fair observation
Record the broadcaster, feed edition and clock. Choose a distinct moment such as the start of a replay, then record when it appears on each screen. A schedule saying the event starts at 20:00 does not identify the delay in live playback.
Use the result
If one service plays smoothly but behind, it may be an intentional tradeoff between buffering and immediacy. If the delay grows during the programme, note whether the player stalls or catches up. That is a different observation from a stable delay.