For those who are interested:
Per the Catholic Encylopedia concerning the LXX:
"It is not possible to determine accurately the precise time or the occasions on which these different translations were made; but it is certain that the Law, the Prophets, and at least part of the other books, that is, the hagiographies, existed in Greek before the year 130 B.C., as appears from the prologue of Ecclesiasticus, which does not date later than that year."
The oldest mss of the LXX date from the 4th century AD, same source:
"The three most celebrated manuscripts of the Septuagint known are the Vatican, "Codex Vaticanus" (fourth century); the Alexandrian, "Codex Alexandrinus" (fifth century), now in the British Museum, London; and that of Sinai, "Codex Sinaiticus" (fourth century), found by Tischendorf in the convent of St. Catherine, on Mount Sinai, in 1844 and 1849, now part at Leipzig and in part in St. Petersburg; they are all written in uncials."
http://www.newadvent.org/cathen/13722a.htm
Although this sets an end date (latest it could have been written), it doesn't established when the book of Daniel actually was written. The biggest problem is that all these sources form a series of dominos (i.e. Daniel was written before the LXX, but when was the LXX translation done? etc.)
Once again the CE concerning when Daniel was written:
"Over against this time-honoured position which ascribes to Daniel the authorship of the book which bears his name, and admits 570-536 B.C. as its date of composition, stands a comparatively recent theory which has been widely accepted by contemporary scholars. Chiefly on the basis of historical and linguistic grounds, this rival theory refers the origin of the Book of Daniel, in its present form, to a later writer and period. It regards that apocalyptic writing as the work of an unknown author who composed it during the period of the Machabees, and more precisely in the time of Antiochus IV, Epiphanes (175-164 B.C.)"
Was the book written by Daniel or by a psuedo-Daniel at a later time period? Or has the original book of Daniel been "edited" by a later scribe? Depends on "faith". If a "prophet" can't possibly "predict" the future, then the book "must" have been written after the events described, which necessitates a later date. What ones believes ("faith") dictates how one will interpret the data, in this case.