During development, the length of each cell cycle is tightly regulated. The cell cycle timing has an impact on cell fate and ultimately the development of the whole organism. However, how changes in cell cycle duration control cell fate remains elusive. In C. elegans embryo cell cycle asynchrony is very robust, suggesting that it is important for embryonic development. However, the consequences of losing this asynchrony on cell fate and development of embryos are not known. Here we study a viable mutant of MEX-5 in which PLK-1 remains asymmetrically localized. After depletion of mex-6 these mutant embryos are unable to drive anterior localization of PLK-1, divide synchronously at two cell stage, regain asynchrony at four cell stage and are embryonic lethal, PIE-1 is symmetrically localized at two cell stage and shows dynamic localization patterns at later stages. We observe normal establishment of upstream PAR polarity.