The way I understand it thus far is for 490 years the Jews did not give their land a Sabbath year of rest so that was 70 years they owed God for the land Sabbaths. They went into exile to Babylon and that paid that debt. Daniel 9 speaks of six things they must square away for the 490 years that are determined for them. 69 weeks of years were fulfilled and the 70th week of years is coming up after the Church Age, what we nick name the 7 Year Tribulation Period. What is it that makes the 490 years still on the clock for them since they served the 70 years for the land Sabbaths in exile already?
The Bible contains four such periods in Israel’s history. Each one was actually longer than 490 years, but some scholars believe that for various reasons God didn’t count some of the the time in each of the periods. I won’t go into all the details here, but the four periods are, 1) Abraham to the Exodus, 2) the Exodus to the First Temple, 3) the First Temple to the edict of Artaxerxes and 4) the edict of Artaxerxes to the 2nd Coming.
The 490 year period during which the Israelites failed to keep the Sabbath for the Land and incurred a 70 year penalty in Babylon was the third one. It ended when Persian King Artaxerxes Longimonus gave Nehemiah permission to rebuild the walls of Jerusalem in 445 BC (Nehemiah 2:1-9). The King’s edict also began the count on the fourth period (known as Daniel’s 70 weeks) which is the one we’re in now (Daniel 9:24-27).