This marks the only on screen appearance of the Delaney twins, who were first mentioned in Time and Again (1995) and have been discussed frequently by Tom and Harry.
Robert Duncan McNeill's pants actually caught fire from the jet pack while filming the Captain Proton scenes.
"Thirty Days" was nominated for an Emmy Award for Outstanding Special Visual Effects for a Series. Star Trek nearly swept the category that year. Also nominated were Dark Frontier (1999)/Dark Frontier (1999), Timeless (1998), and What You Leave Behind (1999). "Dark Frontier" won.
At around 30 seconds into the episode, right after Lt. Tom Paris is demoted to ensign and dismissed to the brig, the melancholy theme being played is Ensign Harry Kim's concerto "Echoes of the Void", which he wrote during the events of the episode "Night", Season 5's first episode, in which Voyager was forced to cross a massive void for over two years.
Pressure at depth is an important point in this episode. The Earth standard of roughly 15psi/30 feet of submersion is dependent on Earth's gravity, which is dependent on Earth's mass. A water sphere one tenth the diameter, and one fifth the density, of Earth would have the same pressure at its center as an ocean depth of about 300 feet has on Earth. Technical (SCUBA) divers routinely hit that depth.