1800s

By the 1800s at the latest the Arcateenians had faster-than-light travel capabilities, including transporter systems and superluminal communications technology. (TV: Greeks Bearing Gifts, Invasion of the Bane)
Openings to Yssgaroth's universe could be found in 1800s in London, near Stonehenge and on the unnamed planet in the Althosian system. (PROSE: The Pit)