Always, or at least whenever you can or whoever is capable. It is a Mitzvah to study science because Moses Maimonides (the Rambam) felt that people should develop themselves and society. People need to go beyond the Torah, to study science and history.[1]

Maimonides wrote, that people should look forward not backward, for we have eyes in front of our faces and not behind our ears.[2]

Rabbi Abraham-Yitzhak Kook, a mystic, also felt that revelation did not cease. It is ongoing. Revelation did not stop with Sinai and the prophets. Revelation is in the hidden work of science revealed to man in a subtle way. Rabbi Ephraim of Sudylkow, the grandson of Israel Ba’al Shem Tov wrote that:

> "Torah is interpreted in each generation according to what that
> generation needs...," and that, "One who denies this is like one who
> denies Torah, G-d forbid.”

The Vilna Gaon also felt that people should study the sciences, writing that at 70 CE Judaism died but was resurrected during the enlightenment.

Additionally, the Bible (Genesis) states that people were made in the image of G-d (that image is the intellect).

[1] Guide 1:1, 3:27, and elsewhere.

[2] In his book on the physician Hypocrites.