Two-and-a-Half Month Gap
The Two-and-a-Half Month Gap took place over the summer of 1992.
Back in the day, before Internet service was widespread, most people on Usenet got their access through university connections. Thus, the Cosmic Plot Device Caper was cut off by the end of the school year, as most of those who had participated left for the summer. Two and a half months later, Scavenger posted the Call to Arms, bringing the LNH back together.
In-continuity, this is the time period during which Beige Noon took place, altering continuity and serving as a symbolic division between the pre-Gap LNH and the post-Gap LNH.
Out of continuity, it was a parody of the Five-Year Gap from the dark-n-gritty dystopian sci-fi relaunch of the Legion of Super-Heroes, done by Keith Giffen and Tom & Mary Birnbaum in the early 90s. (This also helped inspired the post-LNH20 Comics Presents #21 status quo of LNH20.)
The immediate post-Two and a Half Month Gap period was the time of maximal narrative chaos for the LNH, as various people tried to pick up the old add-on threads that became the CPDC. Characters were added, dropped, and shifted between different incompatible plotlines with wild abandon. Others such as Continuity Champ and Plotchopper were introduced to sort out the plot or explain its errors. By the time the Cry.Sig and 501 Blues: The Long Road to Nowhere were finished, things had been more or less sorted out, but trying to make sense of some of the references in early stories will give you a headache.