It is the third time that he told us about his story.
It was the third time that he had told us about his story.
这是固定句型.it isthe first/ second/ third time that sb. did sth. 这是某人第几次做这件事情了.
如果be动词是一般现在时,从句中的谓语动词用过去时.
如果be动词是过去时的话就用过去完成时.
所以选B