Substantial Completion......?

I am working on a large manufacturing project aiming for LEED Silver. The project is being completed by area and COs will be issued for each area. Areas are defined by particular processes that will be performed in that area during the manufacturing process upon completion. My question is, what in this case, is substantial completion? Would it be after the final CO is issued, can it be a judgement call from the design team? In this case, what constitutes substantial completion and when the 24month clock begins to tick? Thanks for the help guys!