Advanced ticket booking

no, it's not correct, students during summer holidays can buy tickets online 30 days in advance, ordinary customers can buy tickets online 20 days in advance and everywhere else at the railway station or ticket office should be possible to book tickets 18 days in advance although there might be case of specific train, which can have different conditions, although ajority of trains share what I wrote in first paragraph or maybe you misunderstood them and maybe all tickets were sold out and they told you to try to come later if someone cancelled their tickets or maybe they have some quota of tickets they run off for this train and they should have more from this quota available again 3 days prior departure.