And while it is mathematically possible to identify grand duke afflictions on a day-to-day basis, the attention is focused on the year as it is generally agreed to be the most potent.
However in date selection, the yue po (月破) a.k.a month breaker is a more potent negative force compared to the year breaker.
This is because bazi is usually used as a central point of focus when selecting auspicious days to conduct specific activities.
And with bazi concepts, the closer a character is to the self element (day master), the more influence it has on it.
As the year breaker is based on the year pillar’s earthly branch and the month breaker based on the month pillar’s earthly branch, simple observation of a bazi would tell you that the month branch is in a much closer position to the self-element than the year branch.
The yue po is identified by identifying the month branch. Then associating the month branch with the grand duke, the character opposite this branch would be the yue po.
For example, most of october would have E11 as the month branch. As E11 is the dog zodiac, the conflicting zodiac would be the dragon zodiac E5. So by referring to the Hsia calendar, any day with the E5 element during the month of E11 would be a bad day to commence something important like the first day of business.
Legend of earthly branches can be found here.
Table of yue po (month breaker)
It is absolutely not advisable to schedule any activities on month breaker days (月破日), especially when failure can definitely bring disaster.
This includes things like surgeries, huge investment decisions, moving into a new house, etc.