It is midnight between 1 1 and the next morning 1. The arrangement of the eight characters will involve the morning and evening. Also consider the solar terms of the day, some people will be born around the solar terms. Those born before the solar term shall be subject to the previous solar term, and those born after the solar term shall be subject to the latter solar term. So I suggest you check the perpetual calendar to see if the seventh and eighth days of your birth involve solar terms. If it doesn't involve it, it will be the eighth grade.