Complex sentence: The prospective builders, Broad Sustainable Building, estimated it would take just 90 days to construct, but this is not counting 120 days of prefabrication before on-site work commences; the total schedule is 210 days.
Split into simpler sentences: The prospective builders, Broad Sustainable Building, estimated it would take just 90 days to construct. Including 120 days required for prefabrication before on-site work commences; the total schedule is 210 days.