Weekend and holiday dates sell out fast. The likelihood of getting such tickets are slim at best. If you can at all, please choose a weekday date.
Sumo is an all day event starting at 10:00 am. The morning begins with lower ranked bouts that get progressively higher. The "main event" starts at around 3:00 pm with the entrance ceremony of the top ranked Sumo.
The top Sumo then battle from around 3:30 to the end of the day at 6:00 pm, with the highest ranked match-up as the finale.