I can offer up the Mormon perspective on these verses. The Book of Mormon has a wonderful explanation of the purposes and the nature of creation in the Book of 2 Nephi.
10 And because of the intercession for all, all men come unto God; wherefore, they stand in the presence of him, to be judged of him according to the truth and holiness which is in him. Wherefore, the ends of the law which the Holy One hath given, unto the inflicting of the punishment which is affixed, which punishment that is affixed is in opposition to that of the happiness which is affixed, to answer the ends of the atonement—
11 For it must needs be, that there is an opposition in all things. If not so, my firstborn in the wilderness, righteousness could not be brought to pass, neither wickedness, neither holiness nor misery, neither good nor bad. Wherefore, all things must needs be a compound in one; wherefore, if it should be one body it must needs remain as dead, having no life neither death, nor corruption nor incorruption, happiness nor misery, neither sense nor insensibility.
12 Wherefore, it must needs have been created for a thing of naught; wherefore there would have been no purpose in the end of its creation. Wherefore, this thing must needs destroy the wisdom of God and his eternal purposes, and also the power, and the mercy, and the justice of God.
14 And now, my sons, I speak unto you these things for your profit and learning; for there is a God, and he hath created all things, both the heavens and the earth, and all things that in them are, both things to act and things to be acted upon.
15 And to bring about his eternal purposes in the end of man, after he had created our first parents, and the beasts of the field and the fowls of the air, and in fine, all things which are created, it must needs be that there was an opposition; even the forbidden fruit in opposition to the tree of life; the one being sweet and the other bitter.
16 Wherefore, the Lord God gave unto man that he should act for himself. Wherefore, man could not act for himself save it should be that he was enticed by the one or the other.
In the Mormon view, it isn't necessary to have actually sinned to claim that 'knowledge of good and evil' but merely to have been enticed by sin (else how could Jesus have claim to know our suffering and yet remained sinless?). Adam and Eve, having eaten of the fruit, had progressed beyond simply being and had become self directed, 'agents unto themselves, able to act rather than be acted upon'. They were ready to begin their mortal sojourn.
21 And the days of the children of men were prolonged, according to the will of God, that they might repent while in the flesh; wherefore, their state became a state of probation, and their time was lengthened, according to the commandments which the Lord God gave unto the children of men. For he gave commandment that all men must repent; for he showed unto all men that they were lost, because of the transgression of their parents.
22 And now, behold, if Adam had not transgressed he would not have fallen, but he would have remained in the garden of Eden. And all things which were created must have remained in the same state in which they were after they were created; and they must have remained forever, and had no end.
23 And they would have had no children; wherefore they would have remained in a state of innocence, having no joy, for they knew no misery; doing no good, for they knew no sin.
24 But behold, all things have been done in the wisdom of him who knoweth all things.
25 Adam fell that men might be; and men are, that they might have joy.
I apologize for the length of the quotes but they are my favorite in all of scripture. God's intent in the creation of men is that they might know joy and all the commandments and instructions we receive from God are geared toward teaching us to follow the path that leads to joy. Adam and Eve partaking of the fuit was anticipated and was a part of God's plan (how could anything that comes to pass not be anticipated by One who knows all?).
We aren't told how long Adam and Eve spent in the garden. It could have been days or weeks or many millenia. We aren't told how long it took the serpent (Satan) to convince Eve to eat of the fruit, though it's my personal feeling that we have been given only a synopsis of what must have been a long series of conversations. Having eaten they became aware of and subject to the temptations of sin, capable of experiencing grief and therefor joy, sadness and therefor happiness, fear and therefor faith. And they were cast out of the garden and into their mortal probation.