A bill is payable at a determinable future time within the meaning of this Act which is expressed to be payable -
(1) At a fixed period after date or sight.
(2) On or at a fixed period after the occurrence of a specified event which is certain to happen, though the time of happening may be uncertain. An instrument expressed to be payable on a contingency is not a bill, and the happening of the event does not cure the defect.