Sentence:  recommend to the Congress <WSD>from</WSD> time to time authorization for construction and operation , or for participation in the construction and operation , of a demonstration plant for any process which he determines , on the basis of subsections ( a ) and ( b ) above , has great promise of accomplishing the purposes of this Act , such recommendation to be accompanied by a report on the size , location , and cost of the proposed plant and the engineering and economic details with respect thereto ; 
Meaning of the word marked with <WSD> tags:  now and then or here and there