There is nothing in the NRCoT which explicitly defines the cutoff for timetable changes, although they do purport to limit delay compensation claims to being based on "the arrival time shown in the timetable in place on the day that you travel".
This is so poorly defined (what source is taken as a reference for what's "shown" in the timetable, and what does "in place" mean?) that it is difficult to pin down a clear definition.
Furthermore:
- The NRCoT can't exclude the minimum level of compensation payable under the Passenger Rights and Obligations Regulation (PRO) - Article 6 of the PRO refers. This is a minimum of 25% or 50% of the one-way fare for a 60-119 or 120+ minute delay (respectively), provided this amount exceeds a minimum threshold of €4 (≈£3.32). Obviously this is much less generous than the normal Delay Repay provisions, but it is at least something.
- The NRCoT are subject to the provisions of consumer law, particularly in terms of them being liable to be excluded if they are unfair. I've previously talked about this but in essence, I would regard the relevant NRCoT condition to be unfair insofar as they purport to allow the trader (i.e. the railway) to unilaterally vary the essence of the contract (which in the context of a rail journey would include the timings) without actually notifying you, let alone doing so on the day the service is to be provided.
In practical terms, submit a Delay Repay claim and if this is rejected, let us know and we can advise you on how to proceed. Suffice it to say, a claim rejection is not at all the end of the matter.