Other benefits of melatonin include general neuroprotective effects, as melatonin is a powerful antioxidant. Melatonin also has several anti-cancer properties, and is currently being investigated for its role in fighting breast cancer.
The date of substantial completion is extremely important, because it determines the date that a contractor is no longer fully liable for delayed completion or for minor incomplete details. After substantial completion, the owner again becomes responsible for the property, i.e., security, utilities, etc.
It depends on the context. Commencement of tenancy inside a particular lease will generally refer to the start date of that particular lease. In other contexts it can mean the date when the tenant moves in, or the date of the first lease between the tenant and landlord (even if that lease was subsequently renewed.)