To me the idea would seem somewhat understandable for an advanced alien species terraforming a planet - It will take some work. If we're talking some all powerful god entity I would have thought 6 gazillionths of a nanosecond would be sufficient.
From a biblical perspective it took 6 days and required a rest at the end.
And on the 8th day, God turnith to his client and spaketh, "That will be tree-fitty."
The whole "7th day being Sunday" sadly results from uninformed chauvinism; the Jewish calender was sufficiently different from ours. In fact, their calender started on Sunday, meaning the Sabbath would have actually been on Saturday.
But all of this is meaningless drivel anyway, who cares really? The Sabbath is about as useless of a religious tool as fasting (Jesus didn't even respect it). I've heard several interpretations of these "days" as symbolic and they supposedly represent much greater lengths of time than our "days". This is supported (weakly) by sparse verses here and there (2 Peter 3:8,10; Ezekiel 4:4-6). These verses nicely clean up some early contradictions (i.e. God: "If you eat of the tree, this day you will surely die."...and Adam was kicked out, not dead that very day. Well now a day constitutes as 1000 years, so He is all of a sudden right on as usual). Sounds like somebody can't pick up on figurative language.
Speaking of figurative language, there is another view; that the Sabbath isn't a period of 24 hours that is magically more pious than any other set of hours, but a state of spirituality in relation to God, as are all the other "days". This interpretation recognizes the absurdity of the literal words of the Bible, and so cloaks it in a shroud of metaphor (as if this is somehow better). Some are ambitious enough to play theological connect-the-dots to such an extent that they claim the first chapter of Genesis is actually a microcosm of all of time (which also nicely piffles the contradictory and adjacent two accounts of creation in Genesis); the seventh day a day of "rest" because by this time, Jesus has returned (once again, not literally, but spiritually in his people to such an extend that you might as well be looking at a physical Jesus) and the Earth experiences a Golden Age of revelation and harmony with God.
Of course, I don't buy into any of that either
