The Government shall have the right to elect to occupy the space in partial increments prior to the substantial completion of the entire leased premises, and the Lessor agrees to schedule its work so as to deliver the space incrementally as elected by the Government. The Government shall pay rent commencing with the first business day following substantial completion of the entire leased premise unless the Government has elected to occupy the leased premises incrementally. In case of incremental occupancy, the Government shall pay rent pro rata upon the first business day following substantial completion of each incremental unit. Rental payments shall become due on the first workday of the month following the month in which an increment of space is substantially complete, except that should an increment of space be substantially completed after the fifteenth day of the month, the payment due date will be the first workday of the second month following the month in which it was substantially complete. The commencement date of the firm lease term will be a complete determined from all rent commencement dates.