They arrived one day apart or at least on different dates?

Are they on different sides of the platform?

They are going different directions

Maybe 12 hour apart … but then you say “at the same moment” … hmmmmm

My vote is opposite directions. At least where I live, a train can be heading north and south and share a central platform.

*a train can be headwind north and ANOTHER train heading south and both share a central platform. Not the same train heading both north and south lol.

Another option of course is that one train is pushing/pulling the other- such as a mechanical failure or some types of cargo train. There may be some semantics involved as to wether the trains are coupled or not and would be considered a single train with multiple engines or how we want to parse that- but semantics can be involved in the platform answer too as it depends on wether each side servicing a train is considered by its own platform designation or wether it is considered a side of a single platform.

Here’s the answer: same time (or moment-say 6 AM) at AM and PM!

Nice one!

Well played.