So is the reason that you found the first one unnatural because "after" was used in future tense?The second and third have the same meaning for me.
The first one is not very natural. Usually I would say: "The train will arrive in 2 hours."
There really isn't anything wrong with using "after" and the future tense. I think the part of the sentence that is unnatural for me is the use of "after" plus a specific time period.
After I finish washing the car, I will cut the grass. :tick:
After two hours, I will cut the grass. :cross:
There may be other contexts in which this will work, but the original train sentence is not good.
Yes.