finish、the、on time这些都没问题,有问题的是hardly were.
应改为：They were hardly able to finish the difficult job on time.
hardly意为“几乎没有,几乎不”,是副词,常位于实义动词之前,系动词、情态动词和助动词之后.hardly本身含有否定意思,在表示否定意义的句子中不能与no,not,none等否定词连用.hardly并不是hard的副词形式.hard既可以作形容词,又可以作副词,意为“困难的（地）；艰苦的（地）”.