In the 22nd century, after the Enterprise NX-01 destroyed a Borg ship, Doctor Phlox told Captain Archer about a subspace message he was receiving when he was infected by the Borg's nanobots. The numeric sequence of that message was decoded to the spatial coordinates of Earth, which led to the conclusion that they were sending the location of Earth to their home world. Archer also decoded the location to where the message was being sent, it was somewhere deep in the Delta Quadrant. Then, T'pol said that it would take at least 200 years for a subspace message to reach Delta Quadrant. And, Archer replied something similar: "Sounds like we have just postponed the invasion temporarily until 24th century."
Now, my question: It was Archer's first encounter with Borg and he didn't even know the name of their race. There wasn't even any evidence of them in the Vulcan database. So, he didn't know anything about their Transwarp Conduit / Transwarp Corridor. It was normal to think like this: "The subspace message would reach their home world in 200 years. Then, they would start their journey to Earth. As the speed of warp vessels was less than the speed of subspace transmission, it would take at least another 200 years to reach Earth." So, with normal thinking, it should be the 26th century. But Archer concluded it would be the 24th century. How?