Using the ‘Later trains’ button at the bottom of the Live trains tab results, it’s possible to find trains up to around 24 hours into the future. And using the ‘Earlier trains’ button, which appears if you drag down from the top, you’ll be able to find results going back around 20 hours or so.
When Railboard searches for earlier/later trains, it searches 12 hours backwards/forwards from the earliest/latest train currently in the results. If no trains are found, you’ll be presented with a message to let you know.