I see the time periods you referenced as referring to the same era. So that the various events described take place during the same time period of 1260 days (3.5 years, or 42 months).
As for the structure and layout, the book follows several patterns which interact:
1. Calendrical. Seven trumpets likely corresponding to the first 7 months of the Bible calendar. Each month a trumpet was sounded at the new moon, the feasts all take place within the first seven months.
2. Passover. The trumpet and bowl judgments reflect the plagues during Passover and the Exodus.
3. Liturgy. The book has many elements of both the Passover, Atonement, and Tabernacles feast liturgies and themes. The book often appears to reflect a divine liturgy or worship service in heaven with corresponding effects on earth.
And of course, numerous themes from old testament prophecy are interwoven throughout the book.
As for interpretation, it then seems obvious to me that it must be "unlocked" by the aforementioned old and new testament data.
But one hindrance is this:
Revelation 10:1-4 KJV
And I saw another mighty angel come down from heaven, clothed with a cloud: and a rainbow was upon his head, and his face was as it were the sun, and his feet as pillars of fire: [2] And he had in his hand a little book open: and he set his right foot upon the sea, and his left foot on the earth, [3] And cried with a loud voice, as when a lion roareth: and when he had cried, seven thunders uttered their voices. [4] And when the seven thunders had uttered their voices, I was about to write: and I heard a voice from heaven saying unto me,
Seal up those things which the seven thunders uttered, and write them not.
There are seven seals, seven trumpets, seven thunders, and seven bowls. The seals, trumpets, and bowls are described in detail, but the thunders are not. What happens during those seven thunders? We are not told. Since the vision is intentionally incompletely transmitted to us, the interpretation must of necessity be incomplete also.