What is the 2520 Year Prophecy?   

It is the longest time Prophecy in scripture.

 Where is it and who found it?

By Miller who started  his studies in Genesis and went systematically through scripture comparing verse to verse and making sure each word had its bearing. It was in this way he formalized his understanding of prophecy first was the 2520 because it was in Leviticus and then the 2300 years in Daniel, in addition to Islam and more. By 1833 he had formalized his message, when he had received his first invitation to preach. As noted above it is given to us in Leviticus 26.

 Does it affect the 2300 year prophecy?

 No it does not in fact it confirms the 2300 year prophecy and it becomes witness unto it.

 Why have we not heard more about it?

 For Adventists it is a new (but old) and an old thing for the rest of the world, just type in 2520 year prophecy and see what you get. An interesting note, the 2520 was actually a new discovery and as Miller gave his presentations it shook the world for it pointed to the nearness of the Advent of Christ.

 When & why was the 2520 forgotten in the SDA Church when it was a part of it in the beginning?

 That is a good question and requires a in depth study to tell it all but a short answer goes something like this. There is not an exact date per-say but it was more of a process of abandonment. As they (Millerite/ SDA movement) struggled with various issues one of them was the use of the then 1850 Chart which was a repeat of the 1843 Chart but modified to include the sanctuary message and the 3 Angels Message of  Revelation 14 along with other information from the 1843 Chart.  Both of these Charts have the 2520 on it and it was used by all the Millerite preachers of that time the only thing that was changed was 1843 to 1844. The process of abandonment started back in the late 1860's. From 1903 to about 1907 Sister White issued a series of warnings that we have no new message.... Meaning the message from 1840-44 was to be preached which included the 2520, Daily, Islam and so on. There were several  controversies  brewing in Adventism during that time.  Then from 1908 to 1910 she issued a stern warning to the parties involved with the controversy since they had not moved into the message the way they were supposed to (Righteousness by Faith and 1840-4 msg) it was then more important to have unity in the Church then to bring separation. After the passing of Sister White the abandonment  was pretty much on its way by the time most of those who had been originally involved with the message had passed away it was no longer being preached though some still kept  it.

Interestingly enough I have personally met people from different parts of the world that were taught the 2520 with the 1843 Chart to my surprise. In countries from Africa and what is now Romania and other places. I suspect that there may have still been people here in the States that taught this but it is not until recently that it is now coming back into the full light it deserves an indicator that this message is the last message and is as Sister White tells us that we have no new message. Here is one of those many quotes: 

     We have, as had John, a message to bear of the things which we have seen and heard. God is not giving us a new message. We are to proclaim the message that in 1843 and 1844 brought us out of the other churches. We need the Holy Spirit to kindle in our hearts the zeal and earnestness that were then seen among God's people. I thank the Lord that there are still living a few who can remember those days, and who know whereof they speak.  {RH, January 19, 1905 par. 22}

Want to learn more?