Jewish Encyclopedia: Hillel: "His activity of forty years is perhaps historical; and since it began, according to a trustworthy tradition (Shab. 15a), one hundred years before the destruction of Jerusalem, it must have covered the period 30 BC–10 AD"
jstor.org
See page 239 in Carmichael, Calum M. “Laws of Leviticus 19.” The Harvard Theological Review, vol. 87, no. 3, 1994, pp. 239–256.