How far in advance do the train times appear on the app?

Hi, I’m planning on going interailing later this year, and I’ve had a brief look at the interail planner app. There’s a particular journey I plan on making (Nice-Milan) and for every single day, there are various options of trains all about 5hrs long. However, when you skip into May 2024, there either aren’t any trains available or there is one but it’s 20hrs long. Is this just because we’re too far away to book, or is it genuinely true that there aren’t trains that take 5 hours in May??