And to repair Chessed-Gevurah-Tiferet so that Chochmah-Binah-Daat may be revealed over them requires the entire period of Suckling… This is clear from the teachings of the ARI of blessed memory about the mystery of the thirteen years and one day. (The term Suckling here refers to the entire period of thirteen years until Maturity.)
…for they are thus steadily drawn down in stages in the necessary way. It is the gradual, stage-by-stage developmental process that determines the time period. The stages in any given case depend on factors intrinsic to that case and the time involved is measured according to that specific gradation. As a general rule, wherever we find a time period specified for some given process, we know that this is the gradation required because of the intrinsic nature of the aspect involved.