Each Warrant Agreement shall specify when it is exercisable. The total number of Shares subject to a Warrant may, but need not, be allotted in periodic installments (which may, but need not, be equal). A Warrant Agreement may provide that from time to time during each of such installment periods, the Warrant may become exercisable (“vest”) with respect to some or all of the Shares allotted to that period, and may be exercised with respect to some or all of the shares allotted to such period or any prior period as to which the Warrant shall have become vested but shall not have been fully exercised. A Warrant may be subject to such other terms and conditions on the time or times when it may be exercised (which may be based on performance or other criteria) as the Administrator deems appropriate.