Thanks for the suggestions guys, but since I am doing it for fun, part of the challenge is to see if I can optimize a route myself, especially by taking some out of band transport to optimize stops vs. distance (e.g. taking a minibus from Tsuen Wan West to Tsuen Wan)
Otherwise its pretty easy to get the raw timing information from API and apply a search algorithm to it, which would have the benefit of being 100% accurate (as opposed to an LLM).
Of course, you also need to ensure that no stations will be closed on the Sunday you decide to do it, as usually if there is works going on they will do it on a Sunday.
And hope for no incidents that temporarily close stations, which seems to happen quite a bit on the East Rail line, although probably less so with most stations having platform barriers now.