This is the first time in which the Delaney sisters are mentioned. They are discussed by Tom and Harry throughout the series but only ever appear on screen in Thirty Days (1998).
Outdoor scenes were shot at the Tillman Water Reclamation Plant. The plant's Japanese garden, normally seen in many other Star Trek episodes shot at the plant, is not seen this time, but rather the industrial-looking front part of the main building is shown.
Several set pieces seen here were used in previous Trek series. The street lamps were seen on Romulus and Rutia IV, a large wall on the marketplace was originally a secret doorway on the Amargosa observatory in Star Trek: Generations (1994), the polaron generator was previously seen as an alien field generator in Birthright, Part I (1993), the bomb is the same prop as the one used by Ansata terrorists in The High Ground (1990), and the utility corridor where the climax occurs is the same set used for the service conduits of the Enterprise-A in Star Trek V: The Final Frontier (1989) and for the corridors of the Klingon ship when Worf fights and kills Duras in Reunion (1990).
This is the second episode in a row that deals with temporal mechanics.
The initial idea for this episode involved speculation regarding the controversial Bombing of Dresden in World War II.