Hang on a mo'....Graham you are right. However....
It’s 18.14 - auto announcement of the cancellation of the 18.24 Plymouth train: “Passengers for Bristol Temple Meads - your next fastest direct service is the 18.46 service to Warminster. Passengers for Taunto and stations to Plymouth, your next fastest direct service is the 19.22 to…”
So, at the point that the 1824 was announced as cancelled (1814), the next fastest train was ....still the 1816, regardless of the state of the 1824 then? Or did the 1824 overtake the 1816 on a standard day? I'm confused before even trying to work out part 2.