JSON file located in %APPDATA%\WhitePawGames\timetables . The file present is the default timetable on initial launch.
Just edit the file and save and it should load on relaunch as the current loaded timetable. If you want to revert it just delete it. Current values to change are `arrival_time`, `destination`, and `from_instrument`. Other values should stay the same for now - but are placeholders for future variables.