Why is Galus Edom So Long?

It occurred to me that we have never examined in detail why Galus Edom is longer than the punishment for Mechirat Yosef.  (That is to say specifically why Galus Edom is so long, even though it has been explained why there are 2503 of Galus; All non-Beit HaMikdash time after Yetziat Mitzrayim combined)

As brought before from the Zohar Chadash Maamar Mechirat Yosef, the punishment meted out on Am Yisrael for Mechirat Yosef is calculated like this:

• 22 years that Yosef didn't see his father
• 10 tribes that caused the sin
• 7 times the punishment, per the pasuk in Vayikra "seven upon their sins"

22 * 10 * 7 = 1540 years.

And these 1540 years begin in the year 3826, completing in the year 5366.

But that leaves us from the year 5366 until 5783 that the Galus continues.  From where are these 417 years?

The 417 years is slightly less than the 420 years of the 2nd Beit HaMikdash, hinting at the period of Ezra, perhaps the 1953 years should have really started in the time of Ezra.

We have the following in the Talmud Bavli Masechet Yoma 9b

ריש לקיש הוי סחי בירדנא אתא רבה בר בר חנה יהב ליה ידא א"ל אלהא סנינא לכו דכתיב (שיר השירים ח) אם חומה היא נבנה עליה טירת כסף ואם דלת היא נצור עליה לוח ארז אם עשיתם עצמכם כחומה ועליתם כולכם בימי עזרא נמשלתם ככסף שאין רקב שולט בו עכשיו שעליתם כדלתות נמשלתם כארז שהרקב שולט בו

Reish Lakish was bathing in the Jordan River.  Raba Bar Bar Chanah came and gave him his hand (to help him out of the water).  He (Reish Lakish) said to him: By G-d I hate you (the Jews of Babylon in general), as it says (Shir HaShirim 8) "If it is a wall, we will build upon it a turret of silver, and if it is a door, we will enclose it with a boards of cedar."  If you would have made yourselves as a wall and all of you had come up in the days of Ezra, you would have been likened to silver, which does not rot.  And now that you came up (as you have), you are likened to cedars, which are subject to rotting.

The historical context is there as well.  The return to Eretz Yisrael began began in the generations following the end of the 1540 years related to Mechirat Yosef.  We are now in the end of the period related to the Sin of Galus Bavel, the sin of not choosing to come home.