As I understand it, the backend software builds ASDS layers with hourly time stamps of hour 1 - hour 24. These are displayed in AQVx with a daily time line of hour 0 - hour 23.
The ASDS data (whether Tier 2 or Tier 3) are hourly averages, thus hour 1 = average between hour 0 and hour 1 etc.
An interpretation of the AQVx time line is that hour i is either 1/ hourly averaged data (averaged between i and i + 1) ; or instantaneous data (i.e. Himawari-9) which for hour i is the image snapped by the satellite at hour i.
It is recommended that you + we check that the incoming data time stamps are correctly aligned with the AQVx time line.