Temporal evolution of sunspot NOAA AR 11250 (HARP 712 dataset). Top: Snapshots of the continuum intensity selected near the midpoint of each evolutionary phase with I^c/I_QS^c = 0.9 contours. Bottom: Time series of the mean magnetic field strength ⟨B⟩ (solid line) and the field standard deviation (dotted line). The phase is indicated by the line colours. The sunspot exhibits a clear forming, stable, and decaying phases with ⟨B⟩ approaching the invariant value (dashed black line) during the fully developed stable interval. The vertical dashed black lines mark the times corresponding to the snapshots shown in the top row.