I’m not entirely convinced that’s what ends up happening. On the GN, the Cambridge stopping service was timed to take 40 minutes between King’s Cross and Hitchin in 317 days, though to be fair achieving this required *very* slick work from the driver, 42 minutes was more typical. In May 2018 the same journey was timed to take 52 minutes, and in today’s timetable takes 47 minutes with an extra stop.
In practice, in 317 days the train went as fast as possible, and if it got delayed then so be it. Now you either get held everywhere, or delayed if there’s stuff going on. So you simply lose out *all* of the time instead of *some* of it. And in my experience it’s made no real difference to dependability at all.
It’s rather unfortunate that with trains which have better performance, are longer, and supposedly designed for quick boarding and alighting, that we can’t match let alone beat 1990s timings with good old 317s.
Perhaps I’m just a glass-half-empty person!
Having said all that, there’s not much point in having timings which can’t really be achieved in practice.