At approximately day 1

Leydig cell proliferation occurs.

Duration: 6 weeks

Reference [PubMed Link]

Boukari K, Ciampi ML, Guiochon-Mantel A, Young J, Lombes M, Meduri G. 2007 Jul. Human fetal testis: source of estrogen and target of estrogen action. Hum Reprod 22(7):1885-92.