Mark S. Smith argues here that the transition towards monotheism started in 8th century BC as it appears that other texts from surrounding cultures from this period also appear to exhibit monothenizing trends:

Knohl (2017) goes even further back in time and argues that, since there appears to be no evidence of any anthropomorphic figurines or cultic statues in Israel during the Iron I period (c. 1200 – 1000 BC), some form of Israelite monotheism may have already existed during this time period: https://www.academia.edu/35321606/The_Rise_Decline_and_Renewal_of_Biblical_Religion_Orbis_Biblicus_et_Orientalis_283

The predominantly accepted view among biblical scholars posits that Israelite religion developed in a linear fashion, from polytheism to monotheism. This was a gradual shift from the belief in many gods, to the belief in one God, Yahweh, and the complete negation of the existence of all other deities. According to this view, the first stage of this process was the polytheistic stage in which Yahweh was one of a family of Canaanite gods. According to scholarship, this stage is reflected in the version of Moses’ Song as found in the Dead Sea Scrolls and the Septuagint. On the basis of this version of Deut 32:8–9, scholars contend that Yahweh was one of the sons of Elohim, or in other words one the children of El or Elyon (See, for instance, Mark S. Smith, The Origins of Biblical Monotheism (New York: Oxford University Press, 2001), 48–49). A similar argument is based on Psalm 82 (See Smith, Origins of Biblical Monotheism, 48–49, and the recent discussion of Peter Machinist, “How Gods Die, Biblically and Otherwise,” in Reconsidering the Concept of Revolutionary Monotheism (ed. Beate Pongratz-Leisten; Winona Lake, IN: Eisenbrauns, 2011), 189–240). According to these scholars this is evidence that the goddess Asherah was considered to be Yahweh’s consort.

The next stage in the development of Israelite religion is monolatry. It is at this point, as the theory goes, that Israelites were required to worship Yahweh exclusively. This requirement, however, did not preclude the existence of other gods. An expression of this monolatry is evident, for example, in the Song on the Sea, in the expression, “Who is like you among the gods, O Yahweh” (Exod 15:11). This verse and others like it (e.g., Pss 77:14; 89:7) do not deny the existence of other gods; they simply elevate Yahweh above other gods. This monolatrous view is also reflected, perhaps, in the second of the Ten Commandments, in the injunction: “You shall have no gods but me” (Exod 20:2). In this case as well, there is no abnegation of other deities, just a prohibition against their worship (See William H. C. Propp, Exodus (2 vols.; AB; New York: Doubleday, 1999–2006), 2:167). Scholars who accept this paradigm of linear development argue that the standard-bearers of this monolatrous exclusivity were the prophets of the ninth century B.C.E, such as Elijah, Elisha, and their followers in later periods, such as Amos, Hosea, Isaiah, and Jeremiah. This is the “Yhwh-alone” party according to Morton Smith’s Palestine Parties and Politics That Shaped the Old Testament. However, followers in later periods, such as Amos, Hosea, Isaiah, and Jeremiah.5 However, the majority of the Israelites did not accept this command to worship Yahweh exclusively and continued to worship other gods in addition to Yahweh.

The third and final stage according to this paradigm of linear progression is complete monotheism. This stage is reflected primarily in the prophecies of Deutero-Isaiah. At this point in time the existence of all gods is repudiated, except for Yahweh: “I am first, and I am last, and there is no god except for me” (Isa 44:6), “I am Yahweh and there is no god but me…for there is none but me, I am Yahweh and there is none other” (Isa 45:5-6). In this view, Israelite religion reaches its peak at the end of the Babylonian period, after a long period of development.

Kaufmann objected to seeing the issue of many gods as opposed to one god as the defining the main aspect of biblical monotheism. This excerpt accords with Kaufmann’s definition of biblical belief in his book, The Religion of Israel: “The basic idea of Israelite religion is that God is supreme over all. There is no realm above or beside him to limit his absolute sovereignty. He is utterly distinct from, and other than, the world” (Kaufmann, Religion of Israel, 60). He argues that there is no theogony in the Bible. There is no account of God’s coming into being through any material medium and there is no account of God being born. Moreover, the myths of the Bible do not include some of the central motifs of polytheistic legends. God has no family history. God has no father, no brother, and no son rooted in reality or conceived through God’s seed. God does not die or procreate. He is not lustful and does not have sexual relations, nor does he have any sexually conceived offspring (Kaufmann, Religion of Israel, 67–72). The second facet of Kaufmann’s disagreement with the accepted views on the development of biblical religion is the idea of progression. Namely, at the center of the accepted paradigm is a linear development in many stages. According to Kaufmann, Moses was the first prophet who conceived of the basic idea of biblical religion and the first to teach it to the Israelites (Kaufmann, Religion of Israel, 223–31). In Moses’ time the Israelite tribes were in the midst of a religious struggle between monotheistic ideas and the polytheistic practices that had been the norm beforehand. The battle for supremacy was decided quickly and Moses’ monotheism won out. This lightning victory is parallel, according to Kaufmann, to Muhammad’s victory against the idolatrous tribes of the Arabian Peninsula

1. Based on this view, Kaufmann casts doubt on the historical evidence the books of Judges and Kings offer concerning idolatrous practices during the period of Judges and during the monarchy. According to him, and was practiced by a small minority of Israelites. The exception to this was the reign of Ahab, who, under the influence of his wife Jezebel of Sidon, made the worship of Baal the state religion.
2. Which is the case?
3. According to archaeological evidence, about 300 new villages of modest size were built in the mountains of central Canaan over a period of two hundred years, between 1200 and 1000 BCE. Most archaeologists agree that these settlements were built by the first Israelites or proto-Israelites. In the past hundred years extensive archaeological surveys and digs of these settlements were undertaken, and as several scholars have pointed out, the evidence from this period, Iron I, or the period of the Judges is quite surprising: In all of the Israelite settlements of the Iron I period, in the mountains, almost no anthropomorphic statues or figurines were found (See William G. Dever, “Material Remains and the Cult of Ancient Israel,” in The Word of the Lord Shall Go Forth: Essays in Honor of David Noel Freedman (eds. Carol L. Meyers and Michael O’Connor; Winona Lake, IN: Eisenbrauns, 1983), 571–87, esp. 574, 583; Ronald S. Hendel, “The Social Origins of the Aniconic Tradition in Early Israel,” CBQ 50 (1988): 367; Theodore J. Lewis, “Divine Images: Aniconism in Ancient Israel,” JAOS 118 (1998): 36–53, esp. 42–43).

To the best of my knowledge there are only two possible exceptional cases: (1) An anthropomorphic head of a broken clay figurine which was found in Iron I, Israelite Dan; (2) An anthropomorphic bronze statuette which was found within a metal objects hoard under the floor of an Israelite cult room in the Israelite settlement at Hazor. But even this evidence is inconclusive, since there are scholars who claim that in reality the Hazor bronze figurine should be attributed to an earlier non-Israelite period, namely the Late Bronze period (See Dever, “Material Remains,” 583 n. 12; Lewis, “Divine Images,” 43. On the other hand, the entire Hazor cult room was dated by Ziony Zevit to the 10th century; see The Religions of Ancient Israel: A Synthesis of Parallactic Approaches (London: Continuum, 2001), 205). In a recent discussion, based on further excavations in the site, Doron Ben-Ami argues against the possibility that the bronze figurine and the other metal objects were put as foundation deposits before the establishment of the first Israelite cult room at Area B.

This archaeological evidence corroborates Kaufmann’s claim that the monotheistic revolution which banned idols occurred at the beginning of Israelite history and that it is for this reason that we do not find almost any statues or figurines of gods and goddesses in Israelite settlements from the period of the Judges. The Israelites of that period, according to the archaeological evidence, did not represent God with anthropomorphic statues. If one adopts the terminology suggested by Mettinger (Tryggve N. D. Mettinger, No Graven Image? Israelite Aniconism in its Ancient Near Eastern Context), one may say that the Israelite belief of that time was one of programmatic aniconism. It is reasonable to assume that the single aniconic Massebah stone was a symbol of the presence of the single God of the early Israelites—Yahweh.

The virtual absence of anthropomorphic figurines and statuettes from Israelite settlements of the Iron I period and the systematic mutilation of icons at Hazor corroborate Kaufmann’s claim that the religious revolution rejecting idolatry was adopted by the majority of the early Israelite populace. It is therefore also likely that Kaufmann is justified in his opinion that the historical veracity of the biblical sources that claim that the Israelites were idolatrous during the period of Judges is doubtful. It stands to reason that these statements should be attributed to a redactional layer added to the book during a late period. This layer wanted to depict the period of Judges as negative and anarchic: “In those days there was no king in Israel, and every man did as he wished” (Judg 18:1; 19:1; 21:25).