Myelination of axons is the last stage of white matter development which overlaps with early stages of pruning not elicited by experience. Myelination starts early during embryonic stages and continues to early infancy. Myelin-producing cells are considered to date to be responding to intra- and extracellular time cues for the timing of each of their waves and for progressing through their stages of maturation. This chapter shows that the clocks of myelination occur in U-shaped timewise pathways accumulating repeated peaks rather than presenting a simple linear progression throughout gestation. This chapter also integrates data showing that clockwise myelination contributes to accuracy of neural firing more than to its velocity per se. In healthy gestation, myelination clocks are timed and balanced by a molecular complex of positive and negative signaling. The chapter outlines how myelinating cells react to clock genes’ transcription and describes their impact on the redistribution of ion channels, emphasizing clock genes’ modulation of sodium and calcium fluxes. When these molecular events occur in parallel sequences on the vector of time, their timely occurrence secures their healthy integration. Synchronicity occurs during embryonic phases prior to asynchronous firing as the latter includes overlapping myelination and pruning processes from mid-gestation onwards. Stereotyped cyclic behaviors of the embryo are associated with overshooting of synchronous signaling before mid-gestation, and more organized stimulus-related behaviors are associated with asynchronous but more accurate signaling from mid-gestation onwards. Deviations of myelination clocks serve as a risk factor for future neurobehavioral development.