approximate - Humans launch the first warp ships to explore the galaxy. (TNG: "Where No One Has Gone Before")

What is the source for this, the only "300 years" I found in the episode set in 2364 is a future one : "And I calculate that at maximum warp it would take over 300 years to get home!". Is there something else (okudagram) I missed ?
Sorry, just found it : "In three centuries, we've charted just 11 percent of our galaxy." - From Cardassia with pain (talk) 02:31, December 14, 2013 (UTC)