The date of this work is uncertain. Most scholars agree that it is dependent on certain biblical passages, notably Isa 44:9–20, 46:5–7, and thus can be no earlier than 540 BC. Since a fragment (7Q2) was identified among the scrolls in Qumran Cave 7, it can be no later than 100 BC. Further support for this terminus ad quem may be found in a possible reference to the letter in 2 Maccabees 2:1–3.
As mentioned above, the use of “seven generations” rather than “seventy years” points to a later period. Ball calculates the date to be c. 307 – 317 BC. And Tededche notes: “It is well known that many Jews were attracted to alien cults throughout the Greek period, 300 BC onward, so that the warning in the letter might have been uttered any time during this period.”