Stomatal development and patterning provide an excellent system to study molecular mechanisms underlying plant asymmetric cell division (ACD), a process requiring precisely timed cell division and differentiation. The plant-specific protein BASL (BREAKING OF ASYMMETRY IN THE STOMATAL LINEAGE) is polarized throughout stomatal ACD processes, including the precursor cells (where cell division is active) and one of the two daughter cells (where cell differentiation is active). Before ACD, the BASL polarity complex employs the scaffold protein POLAR to recruit the BIN2 GSK3-like kinase family to ensure high cell-division potential in the precursor cells. After ACD, BASL recruits and enriches the components of the Mitogen-Activated Protein Kinase (MAPK) module to specify daughter-cell fate differentiation. Recently, we determined that the BRI1 SUPPRESSOR1-like (BSL) family of Ser/Thr-protein phosphatases as BASL-interacting proteins. The founding member BSL1 colocalizes with BASL in a polarized manner at the cell periphery. We further established that upon the entry of mitosis, BSL1 is recruited to the cortical polarity site and, by joint regulation of the BIN2 GSK kinase and the YODA MAPK activities, functions as a spatiotemporal molecular switch to enable the transition from cell division to cell differentiation during stomatal ACD. Interestingly, the temporal recruitment of molecular activities is coordinated by a cell cycle regulator in the stomatal lineage. Therefore, we propose a model for the spatiotemporal recruitment of polarity proteins governing the progression of stomatal ACD in Arabidopsis.