Eric Nelson said he recently had cause to look over the occupancy permit issued to Westmass Area Development Corp. for the property now known as Ludlow Mills. The date on the document — April 2012 — gave him both pause and more evidence that time does, indeed, fly. Yes, it’s been more than six years since this ambitious project — a blend of both brownfield and greenfield development — was launched, and, for the most part, it is on schedule, said Nelson, president of Westmass for roughly half the duration of this effort. And by on schedule, he was referring to the pace of development, or redevelopment, at this complex of 60 buildings and adjoining undeveloped land. When it started the clock back in 2011 when the property was actually acquired, Westmass said this would be a 20-year project that would generate $300 million in public and private investments, more than 2,000 jobs, and a more than $2 million increase in municipal property taxes.