I'm tentatively thinking the During Action Reports (DARs) should be broken up into the following periods, but I haven't played enough to be sure I'm remembering the eras correctly (or even remembering correctly exactly how many there are). I'll wait a little while to start DAR threads in case anyone has corrections or alternative suggestions.
DAR 1: 4000 BC - 1500 BC
DAR 2: 1500 BC Until Start of Classical Era
DAR 3: The Classical Era
DAR 4: The Medieval Era
DAR 5: The Renaissance Era
DAR 6: The Industrial Era
DAR 7: The Modern Era
Edit: After playing to the start of the medieval era, I decided that having from 1500 BC to the medieval era (in my case 450 AD) in a single DAR was too much, so I'm modifying the DAR structure to have a (likely relatively short in most cases) DAR covering from 1500 BC to the start of the classical era.