Pattern in the availability of SHINKANSEN(highspeed express in Japan)

Hi, I'm NISHIO Hirokazu. I'm now in my hometown Osaka and I must go to my workplace Tokyo before the holiday's end. I checked the availability of the SHINKANSEN and found an interesting pattern. A cross means 'not available', a circle means 'available' and a star means 'no smoking seats'. Green four-leaves icon means first-class seats. Guess why it is available in the third train and not in fourth.



I guess it comes from the arrival time. Typical Japanese company starts at 9:00. The third one arrives at 9:10. It is available. Trains arrives before 9:00 is not available. Those what arrives before 9:09 is available only in first-class seats.