The time period refers to when OT prophets spoke forth the word of God.
The reference about "sawn asunder" refers to a tradition about when King Manasseh ordered the prophet Isaiah to be cut in half.
There is a tradition reported in the Martyrdom of Isaiah (a Christian text from around AD100 which expands on 2 Kings 21) that Isaiah was condemned to death by King Manasseh. Although he hid in a tree, he was found and the tree with Isaiah inside was sawn in half. A similar tradition is recorded in Lives of the Prophets (another Christian text from around AD100). The method of Isaiah’s death (sawn in half) is also supported by the Jewish texts known as the Babylonian Talmud and the Jerusalem Talmud (both written after AD200).
And for a more developed source, there is this.
It is related in the Talmud that Rabbi Simeon ben 'Azzai found in Jerusalem an account wherein it was written that Manasseh killed Isaiah. Manasseh said to Isaiah, "Moses, thy master, said, 'There shall no man see God and live' [Ex. xxxiii. 20, Hebr.]; but thou hast said, 'I saw the Lord seated upon his throne'" (Isa. vi. 1, Hebr.); and went on to point out other contradictions—as between Deut. iv. 7 and Isa. lv. 6; between Ex. xxxiii. 26 and II Kings xx. 6. Isaiah thought: "I know that he will not accept my explanations; why should I increase his guilt?" He then uttered the Unpronounceable Name, a cedar-tree opened, and Isaiah disappeared within it. Then Manasseh ordered the cedar to be sawn asunder, and when the saw reached his mouth Isaiah died; thus was he punished for having said, "I dwell in the midst of a people of unclean lips" (Yeb. 49b). A somewhat different version of this legend is given in the Yerushalmi (Sanhedrin x.). According to that version Isaiah, fearing Manasseh, hid himself in a cedar-tree, but his presence was betrayed by the fringes of his garment, and Manasseh caused the tree to be sawn in half. A passage of the Targum to Isaiah quoted by Jolowicz ("Die Himmelfahrt und Vision des Prophets Jesajas," p. 8) states that when Isaiah fled from his pursuers and took refuge in the tree, and the tree was sawn in half, the prophet's blood spurted forth. From Talmudical circles the legend of Isaiah's martyrdom was transmitted to the Arabs ("Ta'rikh," ed. De Goeje, i. 644).
The irony is Manasseh had carved idols and placed them in the Temple.
And he set a carved image, the idol which he had made, in the house of God,
2 Chron 33:7
The forbidden actions of carving a forbidden idol (Ex 20:4) and carving the prophet of God (1 Chron 16:22) is too terrifying not to mention.