It sounds like the authors have been informed by modern pre-mil dispensationalism as taught in the “Bible Churches”.
From Wikipedia:
the most common list of dispensations is taken from the notes to the Scofield Bible:
* the dispensation of innocence (Gen 1:1–3:7), prior to Adam’s fall,
* of conscience (Gen 3:8–8:22), Adam to Noah,
* of government (Gen 9:1–11:32), Noah to Abraham,
* of patriarchal rule (Gen 12:1–Exod 19:25), Abraham to Moses,
* of the Mosaic Law (Exod 20:1–Acts 2:4), Moses to Christ,
* of grace (Acts 2:4–Rev 20:3 – except for Hyperdispensationalists), the current church age, and
* of a literal, earthly 1,000-year Millennial Kingdom that has yet to come but soon will (Rev 20:4–20:6).
This isn’t about Bible periods or dispensations but about the Covenants of God to man effecting redemption.