Much is made that almost 2,000 years has passed since Christ died, rose, and said He would return. In Preterist thought, the interval of 40 years seems more palatable than one which is of such a great length. Hence, the millennium, i.e., the time in between, is interpreted to be a figurative number representing that 40 years.
It should be noted that the thousand year period in Revelation is, in fact, a figurative number. John adds chiliads to various representative numbers to display the vastness of the number. Hence, the 12 tribes of Israel, each described with the number 1,000, multiplied by the 12 apostles who sit as judges to guide Israel are said to be 144,000 (i.e., a number that represents the church).
The idea here is not that the church is made up of only 144,000 people, nor is it to convey the idea that there are literally 144,000 virgin Jewish men from each tribe that will become Christians, but rather it exists to communicate the idea that the number that belong to Christ, the size of His Church, is vast. The idea is that there are so many that they can be simply represented by a sizable number like 1,000. In other words, the number is figurative and represents another number, but the the number it represents is vastly larger than the literal number itself. It is never used in Revelation of a number that is lower than itself--indeed, such a use would negate the very purpose of the number.
Hence, it cannot be that the number represents 40 years, and indeed, makes more sense that it represents 2,000 or more years instead.
But something else is interesting about which I don't hear a lot of discussion, and that is that the work of Christ is pictured in the Bible, and in early Christianity, as framed by the festivals, especially in terms of the Spring Feasts and the Fall Feasts with an interval period in between that is characterized by harvesting. Christ fulfills, not just certain festivals, but all of them. Hence, His ministry looks more like the following.
Christ's Death (historia salutis) - Passover
Christ in the Grave - Feast of Unleavened Bread (Removing the Leaven from Bread [i.e., removing sin among His people].
Christ's Resurrection - First Fruits (Christ's resurrection is referred to as this in some passages: 1 Cor 15:20, 23;
Pentecost (The Feast of Weeks) - The Holy Spirit Is Given as a Promise of Our Full Future Redemption (This is the day we are in).
The intermediate period between the feasts is harvest time, a time of ingathering. This is likely the time that represents the ingathering of the Gentiles as Christ's.
Proclamation of Victory in the Return of Christ - The Feast of Trumpets
The Full Application of the Redemption Christ has done on the Cross (ordo salutis) - The Day of Atonement (the day where cleansing takes place by applying the blood of the sacrifice to both the people and the tabernacle/temple, which represents all of creation in ANE and biblical society).
The Consummation of the New World at the Wedding Feast - Feast of Tabernacles (a gathering in of the year's final harvest and the remembrance of when we were in the wilderness)
Now, of course, one might take issue with the way these are used here, as the purpose of the feasts in relation to what Christ did are not that explicitly clear, but I do think it is interesting that ingathering of the harvest of Israel's various crops begins around the time of the first feast and ends at the time of the Feast of Tabernacles. If we do make a correspondence here, we might ask why we would consider the current time in which we are living as the consummation of the new world after the Feast of Tabernacles has taken place, rather than the intermediate period where the harvest is still being gathered in, a harvest said not to be completed until Christ returns to gather His elect from the four corners of heaven and earth.
This is really more of a "think about this" argument than it is some knock-down argument, but I do find it interesting at least to think about in terms of how long the millennium might be. If it is characterized by Christ gathering in His elect, then it could actually continue for some time, especially when we take note of the previous idea that the number 1,000 represents a larger amount of X than the literal number represents, not a lower amount of X than the literal number represents.