I know it’s been asked multiple times in the past, but never seems to get any attention from Plex.
The over the air signal in the UK transmits the actual start and end times of programs (in addition to the scheduled times) and DVR devices use this to ensure none of the programme is missed. This caters for early/late starts as well as early/late finishes.
This isn’t currently supported but really needs to be. It is standard PVR/DVR functionality here in the UK and it’s very difficult to treat Plex as anything other than a mildly interesting hobby without it.