The Sixth Day? There is not the slightest hint that John (or the angel of Revelation) was referring to the Creation Week. The cultural context in which the Revelation was written was the Roman Empire with its occupation of Syro-Phoenicia ( which included Israel).
Knowing that the Early Christian Church was enmeshed in Latin (Roman) culture, and since we are dealing with numbers, it would be interesting to look to the Latin form of numbering for a clue to understanding what John was trying to communicate.
Therefore consider what numerical value the Latin letters stand for:
I = 1
V = 5
X = 10
L = 50
C = 100
D = 500
Add these together and we get a total of 666! Does this gematria indicate that no matter who is intended, it is the adversarial Roman Empire that underlies this mystery? Certainly, this rules out all the speculation that prognosticators have engaged in throughout the millennia, who look for a sinister dude in other countries besides Rome.
Even though within the Roman Empire, there were plenty of emperors who qualified for the adversary of Christianity. Some persecuted Jewry, some attacked both Jew and Christian, and one banned the Bible wholesale (Decius, 3021-304). One Apostate emperor leveled and destroyed all the pilgrimage sites in the "Holy Land" in an effort to erase Christianity and set up his own religion.
Some scholars might contend that enough ambiguity was intentionally portrayed in Revelation so Christians of every era would stay alert to external dangers, yet be encouraged in the struggle of extending the Kingdom of Christ. To this I would concur.
Considerations Although most readers use Revelation 13 as a jumping-off place in search of a man, it should be noted that "beasts" in the prophecies represent empires or nations, and not a single person! (horns represent specific individuals). The first beast mentioned in chapter 13 is pictures as having the same animal characteristics of the four beasts in Daniel's prophecies---and it was "nations" that were intended to be interpreted.
Also note that there is no definite article before "man" in this verse. The translation should/could also read "its" and not "his"...etc. (autou, Gk.) And we must not lose sight of the fact that the word, "antichrist," is nowhere to be found here. Nowhere.
These considerations point to 666 (the addition of the six Roman numerals) as a reference to the dominant Roman empire of man at the time of the writing of this book of Revelation. The Roman Empire of Man that deified its rulers certainly had all the dictatorial powers mentioned here.