Standard game times
Weekday night games: 6:00 PM first pitch (most common). Weekend/holiday day games: 2:00 PM first pitch. Weekend night games: 6:00 PM (same as weekday). Some Saturday games start at 2:00 PM or 5:00 PM depending on the team and TV schedule.
Gate opening times
Stadium gates typically open 2 hours before first pitch. For a 6:00 PM game, gates open at 4:00 PM. For a 2:00 PM game, gates open at 12:00 PM. This is important because arriving early gives you time to explore food stalls, buy merchandise, watch batting practice, and find your seats.
When do games end?
Average NPB game length is about 3 hours 10 minutes. So a 6:00 PM game typically ends around 9:00-9:15 PM. A 2:00 PM game ends around 5:00-5:15 PM. Extra-inning games (up to 12 innings max) can add 30-60 minutes. Games tied after 12 innings end as a draw.
Planning your evening
For a 6:00 PM game ending at ~9:15 PM: you have about 2-3 hours before last trains (typically 11:30 PM-12:30 AM). Plenty of time for a post-game meal. For restaurants near the stadium, make a reservation for 9:30 PM to be safe.