Who is the last person regarded as a true prophet in Judaism? What was his time frame?
The Tosefta (Sotah 13:4) writes:
משמתו נביאים האחרונים חגי זכריה ומלאכי פסקה רוח הקודש מישראל
Once the last prophets -- Haggai, Zechariah and Malachi -- died, the prophetic spirit ceased in Israel.
Additionally, the Talmud (Bava Batra 14b) writes:
וחגי זכריה ומלאכי סוף נביאים הוו
Haggai, Zechariah and Malachi were the end of the prophets.
These three prophets were all active at the beginning of the Second Temple period which is around 500 BCE or 350 BCE depending on how you deal with the Missing Years.
The Ibn Ezra (in his introduction to Malachi) writes that Malachi was the last prophet. The Rambam (Maimonides) in Melachim 11:1 implies that the Mashiach (messiah) will be a prophet (since he refers to the "other prophets"). (I think both of them agree, actually, just that Malachi was the last prophet until Mashiach.)