It should spell out the allegory clearly, e.g., Galatians 4 where Paul used the images of the bondswoman/Mt Sinai and the freewoman as allegories of the two covenants; one depicting earthly Jerusalem and other the heavenly Jerusalem. Earthly Jerusalem is in bondage, while the Jerusalem above is free, which is the mother of us all.
Revelation 2 and 3 have no characteristics of a biblical allegory. The notion that they depict dispensations/ages within a dispensation is pure invention.