There are times where you see the phrase "latter days" used, say, in the Pentateuch. One example is at the end of Deuteronomy chapter 4. Now, we need to be careful when we see the term "latter days" that we don't automatically jump ahead to the final, ultimate end of things, such as the eschaton. But in that context, what Moses is warning Israel about, as they're about to enter into the Promised Land, that when they get into the Promised Land, he says that if they disobey God and don't follow what's expected in the Sinai covenant, that ultimately they could get kicked out of the Promised Land and sent into exile. So, what Moses is warning or speaking about is once they've been kicked out of the land, are in exile due to disobedience, what he says though, is there's still hope for those people who have been kicked out of the land, that in the "latter days" they can turn to God and call upon him and bring them back. And of course this is a wonderful glimpse of our God who is willing to not give up on his people, but bring them back and restore them, which lays a great theological basis for who God is, a God who restores, a God who redeems even after sin. That provides a basis for understanding God's later acts in the person of Jesus Christ and what he will do in the end ultimately.