Strength of change of core entropy (y axis) as a function of the time difference between the closest merger and the transformation. The change in entropy dK₀ is measured between the time of the merger and end of the transformation for all halos in TNG-Cluster. Color indicates the lookback time of the merging event. We find that large entropy changes occur only for small time differences, suggesting that mergers identified within ∼1 Gyr prior to a transformation are physically associated and/or drive strong cluster core evolution, while mergers that occur earlier than this time window are unassociated and/or cause weaker changes in core entropy.