establishment period
(1) For purposes of this subsection, the term “establishment period” means, with respect to any State, the period beginning on December 28, 1973 , and ending on whichever of the following dates first occurs: (A) the date of the close of the 120-day period following the adjournment of the first regular session of the legislature of such State which commences after December 28, 1973 , or (B) the date of the close of the 15-month period following December 28, 1973 .