I recently bought some advance train tickets. Three days before departure the departure/arrival was rescheduled (or the timetable changed) for the train to depart/arrive 40/39 minutes later.

Shortly before the rescheduled departure the departure was delayed an additional 30 minutes. The train then accrued a further 60 minutes and a few seconds of delays on the way.

So in total I arrived 129 minutes (2:09) later than expected. The train operator sent out links for claims, saying the delay was 89 minutes, not counting the train being rescheduled a few days before (and claiming the train arrived before it had come to a stop, but never mind, this isn't the Shinkansen). Which to be honest is quite good of them.

I think with three days warning that is OK, but I was curious at what point (how close to the departure) would rescheduling a train actually count as a delay? This is for the Eurostar, but I guess the question is general for UK trains.