After corrected midnight: sect 2 changes the Day Pillar

Thirty minutes later, at 00:15, the day pillar finally advances from Wu-Wu to Ji-Wei. The hour pillar is still within Zi Hour. This closes the sequence: across four records spanning an hour and a half, the hour changed once and the day changed once, at different moments.

The Day Master moves with the day pillar, so this single thirty-minute step changes the anchor of the entire chart. A reader born at 23:45 and a reader born at 00:15 on the same night get different Day Masters and therefore different Ten Gods relationships throughout, even though their birth records are half an hour apart.

That is a striking consequence to state plainly, and it is the reason this category exists as four cases rather than one. It is also the reason to be careful about it: the step is real under the stated convention, and it depends entirely on that convention being the right one for your reading.

It is worth adding that a reader in this window is not required to pick a side in the abstract. The practical move is to read the chart under both conventions and notice whether the difference changes anything you actually care about. Frequently it does not, because the surrounding pillars are unchanged. Where it does, you have found a genuine open question rather than a solvable one.