We must keep the spiritual lessons of the letters, not just figure out prophecies. There are several ways to view them, but the most important is personally.
The notion of church eras in Revelation 2-3 is based on some fundamental errors. Jesus expects that all of us learn from all seven letters.
'The day of the Lord' or 'the Lord's day' is not a reference to the fist day of the week (Sunday) but to the time of Jesus Christ's judgment at His return.
The Feast of Trumpets is a memorial of blowing of trumpets, symbolizing the Day of the Lord, the real war to end all wars, when Christ will subdue the earth.
The phrase 'first day of the week' is used 8 times in scripture, but none does away with the Sabbath nor establishes Sunday as the 'Lords Day.'