For most of the year in 2026, you can book Shinkansen (bullet train) tickets just a few minutes before departure at station kiosks. However, for "Peak Travel Seasons" like Golden Week (late April/early May), Obon (mid-August), and New Year, you should book exactly 30 days in advance as soon as reservations open at 10:00 AM JST. If you are traveling with "Oversized Baggage" (suitcases with total dimensions between 160cm and 250cm), you must reserve a specific "Baggage Space Seat" in advance, as these are limited and often sell out days ahead of time. For regional trains or "Limited Express" scenic routes like the Aoniyoshi or Shimakaze, booking 2–4 weeks early is wise. If you aren't traveling during a major holiday, booking 1–3 days in advance via the Smart-EX app is the "sweet spot" to ensure you get your preferred window seat and avoid the stress of the non-reserved car queues.