But He DID say days:
And there was evening, and there was morningthe second day. (Gen. 1:6)
And there was evening, and there was morningthe third day. (Gen. 1:13)
And there was evening, and there was morningthe fourth day. (Gen. 1:19)
And there was evening, and there was morningthe fifth day. (Gen. 1:23)
And there was evening, and there was morningthe sixth day. (Gen. 1:31)
Thus the heavens and the earth were completed in all their vast array. By the seventh day God had finished the work he had been doing; so on the seventh day he rested from all his work. Then God blessed the seventh day and made it holy, because on it he rested from all the work of creating that he had done. (Gen. 2:1-3)
But He DID say days:
If it were literal days why would he say generations?