Monthly Advancement
月限
One palace per month within the Annual Advancement year, with boundaries set by the Sun advancing 30 degrees at a time.
Monthly Advancement (月限, also 流月) divides the Annual Advancement year into twelve months and assigns a palace to each. The first month sits on the Annual Advancement palace itself; each month thereafter steps one palace counter-zodiacally.
The month boundaries are astronomical, not calendrical. They fall where the Sun reaches the natal longitude plus successive multiples of 30 degrees, so each month runs roughly 29 to 31 days and no boundary coincides with the first of a calendar month.
This is the layer that answers "what happens in February" rather than "what happens this year". A body entering the Monthly Advancement palace — or its opposite or trine palaces — within a given month marks that month out from the eleven around it.