The massive basaltic volcanism of the Imbrian period tapered off and ceased during this long span of lunar time.
From the en.wikipedia.org
Analysis of the lunar samples seem to imply that a significant percentage of the lunar impact basins formed within a very short period of time between about 4 and 3.85 Ga ago.
From the en.wikipedia.org
The Pre-Nectarian period is defined from the point at which the lunar crust formed, to the time of the Nectaris impact event.
From the en.wikipedia.org
Western experts had speculated that the landing-site time had been picked so that Luna could begin operating near the start of a two-week period of lunar daylight.