Christians generally understand that a day in prophecy represents a year, and this is true in a number of cases. To understand the basis for interpreting prophetic days as literal years, we should begin by considering the units of time God ordained: the week of days, the week of years, and the jubilee cycles.

The Week of Days
   
When God created the heavens, the earth, the sea, and everything in them, he established the weekly cycle of seven      days, terminating with the Sabbath (Genesis 1:1-2:3). God saw all that he had made, and it was very good. And there was evening, and there was morning-the sixth day. Thus the heavens and the earth were completed in all their vast array. By the seventh day God had finished the work he had been doing; so on the seventh day he rested from all his work. And God blessed the seventh day and made it holy, because on it he rested from all the work of creating that he had done (Genesis 1:31-2:3). 
     The Hebrew word for "Sabbath" (shabbath) is derived from the Hebrew word for "rested" (shabath) in the above passage.

   The Week of Years

When God brought his chosen people out of Egypt, he established the weekly cycle of seven years, terminating with the Sabbath year for the land: The Lord said to Moses on Mount Sinai, "Speak to the Israelites and say to them: 'When you enter the land I am going to give you, the land itself must observe a Sabbath to the Lord. For six years sow your fields, and for six years prune your vineyards and gather their crops. But in the seventh year the land is to have a Sabbath of rest, a Sabbath to the Lord. Do not sow your fields or prune your vineyards. Do not reap what grows of itself or harvest the grapes of your untended vines. The land is to have a year of rest. Whatever the land yields during the Sabbath year will be food for you-for yourself, your manservant and maidservant, and the hired worker and temporary resident who live among you, as well as for your livestock and the wild animals in your land. Whatever the land produces may be eaten (Leviticus 25:1-7).
                                                      
     The 70 Weeks of Daniel 9-Weeks of Years
     Gabriel's words to Daniel were: 
          "Seventy 'sevens' are decreed for your people and your holy city to finish transgression, to put an end to sin, to      atone for wickedness, to bring in everlasting righteousness, to seal up vision and prophecy, and to anoint the most holy" (Daniel 9:24). 
     A "seven" is a "week." When Gabriel gave this prophecy to Daniel, he did not specify that the 70 "sevens" were to be 70 weeks of days or 70 weeks of years; however, knowing that God established both a weekly cycle of days and a weekly cycle of years, it would be reasonable to test both against this prophecy to see which one fit. 
     Historically, the decree to restore and rebuild Jerusalem (Daniel 9:25)was issued by king Artexerxes in 457 BC. The Holy Spirit descended on Jesus at his baptism in AD 27, making him the Anointed One who was to come (Daniel 9:25). The prophecy indicates that the amount of time between these two events was to be 69 "sevens" (seven "sevens" plus 62 "sevens"). If these "sevens" are counted as weeks of days, this amounts to 483 days, which is less than one and one-half years-not remotely close to the amount of time between the two events. If, on the other hand, the "sevens" are counted as weeks of years, the time      prophesied totals 483 years, which is exactly the amount of time from 457 BC to AD 27. (For anyone who is doing the math, there was no year 0, so 483 years from 457 BC really does extend to AD 27.) 
     The 70 weeks of Daniel 9 are an example of prophetic time correctly interpreted using units of years rather than units of days. These 70 weeks are taken from the beginning of the 2,300 "evenings-mornings" of Daniel 8:14, so they are also counted in units of years. This time period of 2,300 years extends from 457 BC to AD 1844 so that other time prophecies occurring within that range are counted in units of years as well. 
     The 1,000 Years of the Millennium-1,000 Literal Years
     The millennium occurs after Jesus' second coming. Revelation speaks of this as follows: 
          And I saw an angel coming down out of heaven, having the key to the Abyss and holding in his hand a great chain. He seized the dragon, that ancient serpent, who is the devil, or Satan, and bound him for a thousand years. He threw him into the Abyss, and locked and sealed it over him, to keep him from deceiving the nations anymore until the thousand years were ended. After that, he must be set free for a short time. 
          I saw thrones on which were seated those who had been given authority to judge. And I saw the souls of those who had been beheaded because of their testimony for Jesus and because of the word of God. They had not worshiped the beast or his image and had not received his mark on their foreheads or their hands. They came to life and reigned with Christ a thousand years. (The rest of the dead did not come to life until the thousand years were ended.) This is the first resurrection. Blessed and holy are those who have part in the first resurrection. The second death has no power over them, but they will be priests of God and of Christ and will reign with him for a thousand years. 
          When the thousand years are over, Satan will be released from his prison and will go out to deceive the nations in the four corners of the earth-Gog and Magog-to gather them for battle (Revelation 20:1-8). 
     The 1,000 years of the millennium are 1,000 years of literal time. They are not expanded to what they would be if every day they represented were actually a year. 
     There are also a number of time prophecies in Daniel and Revelation (e.g., Daniel 12:7, 11-12; Revelation 9:10; 11:2-3; 13:5) that have not been fulfilled but that must be fulfilled before Jesus' second coming. Most of these, if they were counted in units of years rather than units of days, would put Jesus' coming in the remote future-over a thousand years away.
     Observation, then, tells us that prophetic time is given sometimes in units of years and sometimes in units of days.

     The Jubilee Cycles

     Leviticus 25:8-12 describes the operation of the jubilee cycles, which were based on the weekly cycles of years. Basically, a jubilee cycle began every seven weeks, or 49 years; and the 50th year of the cycle was the jubilee year, which meant that the 50th year of one jubilee cycle was also the first year of the next jubilee cycle. This is explained in the section The Weekly Cycles and the Jubilee Cycles. 

     It is our understanding that a day in prophecy represents a year when the prophecy is fulfilled during the operation of the jubilee cycles, because those cycles were based on weeks of years,  rather than weeks of days. Prophecies that are fulfilled after the cycles come to an end are counted in literal time. To reiterate, the reasons for believing this are as follows: 

         History confirms that the unit of time in prophecies already fulfilled was a year, rather than a day. Examples of this include the 70 weeks of Daniel 9 and the "time, times, and half a time" (1,260 "days") of Daniel 7:25, which extended in history from 538 to 1798. Therefore, under conditions that existed in history, a day of prophetic time represented a year of literal time.

         The Bible contains a number of future and imminent time prophecies that must be fulfilled in literal time. An example that is widely agreed upon is the 1,000 years of the millennium. This tells us that under conditions that certainly exist in the future and that possibly exist now, prophetic time is the same as literal time.

         The jubilee cycles are built on weeks of years, rather than weeks of days. The first time prophecy to be fulfilled was the 70 weeks of Daniel 9, and this prophecy was given in weeks of years. Therefore, as long as the jubilee cycles were in operation, prophetic time periods would be counted in units of years. If the jubilee cycles were ever to come to an end, prophetic time periods would no longer be counted in units of years but in units of days.

     The Number 70 And The End Of The Jubilee Cycles 

Praying with you in your understanding the TIME OF OUR LORD's SECOND COMING!