This story unfolds concurrent with the events chronicled over the course of the first four New Frontier novels, concluding during the period between Fire on High and Martyr, roughly around the end of Deep Space Nine's fourth season.
There seem to be a couple errors there. I'm guessing it should be:
This story unfolds concurrent with the events chronicled over the course of the first four New Frontier novels, concluding during the period between Martyr and Fire on High, roughly around the end of Deep Space Nine's fifth season.
Because, as given, the Historian's Note doesn't make sense.