Well there are a lot of great replies, some guesses, and some scripture, but if we put them ALL together it's quite clear what happened...at least to me lol.
On day one, we know that the heavens and the earth were created, but they were in no means completed. Gen 1:1-2, but we know from Ex chapters 20/31 regarding the Sabbath practice. The Sabbath was the 7th day because EVERYTHING created was done in 6 days, and God rested on the 7th day, chapter 31 says after God said these things (12 chapters), that He wrote all of these in stone with His own finger. He wrote these 12 chapters for Moses, and He didn't stutter. He wrote it in Moses time and understanding, and it wasn't an age, otherwise we should have 6 ages and 1 Sabbath age right? (Well this happens when Jesus returns after 6,000 years since the Beginning and reigns in Jerusalem for 1,000 years). Also, pay attention to the order of creation, flowers rely on two things for survival, sunlight to be fed, and bees and other pollen carrying creations to spread the pollen and procreate other flowers...however flowers were created BEFORE Sunlight, and BEFORE bees, so it could NOT have been ages, only a literal 6 days, He also said "and there was evening and morning, thee first day"...and "thee second day," etc.
In Col 1:16 Paul CLEARLY defines ALL realms as having been CREATED by God, so again reference back to Exodus chapters 20 and 31 and the angels fall EXACTLY into the literal and complete 6 days of creation week.
Also we know 2 things from Ez 28:13-15, first we know it says "...on the DAY you were created." (referring to Lucifer), but we also discover he was "in the Garden of Eden BEFORE iniquity was found in him" so Lucifer and the third of the angels hadn't yet fallen before 6 days was up. As for Job 38:4-7, it says "...ALL the sons of God." which would include Lucifer and a third that later fell, right?
The thing most people miss though, is what was the PURPOSE of creation in the first place? Wasn't it for God to fellowship with man? Well why would He even NEED the angels before they were to help serve mankind and God's relationship? It would be unnecessary, right? It also says we (the saints) will JUDGE the angels in the coming age, I Cor 6:3, they are subject to us, and until the fall, man was above the angels because we could fellowship directly with God (I believe this is the most likely reason of what caused Lucifer to have iniquity, much like Cain had towards Able's fellowship and approval of God). We ALWAYS need to ask important questions about motive, don't we? So what would have made Lucifer jealous BEFORE mankind???
As for angels being "timeless" as is said in a few posts above, explain me this, it says, "they cry, 'Holy, Holy, Holy'" as they keep discovering new aspects/facets/faces of God's greatness, in Rev 4:8 it says, "Day and night they never stop saying, "Holy, holy, holy is the Lord God Almighty, who was, and is, and is to come.'" why then would we think they are outside of time, and they keep learning new aspects of God they didn't know before, or am I missing what it says???
It also says in Gen 6:1-8 it says, "...the sons of God (fallen angels) saw that the daughters of man were attractive and they took as their wives...""....when the sons of God came in to the daughters of man (to reproduce half demon/half man) and they bore children to them...{they} were the mighty men...{And} the men of renown." I believe these spawn of demon were the creatures told about in mythology told down from Noah's sons to their sons and sons of sons, but I could be wrong but I don't think so. After the flood God did SEVERAL things. God limited age, He brought about 4 seasons instead of 2 (summer and winter were now here), He destroyed the ice canopy talked about in Gen 1:6, which protected us all from radiation, and allowed dinosaurs to grow to great sizes, allowed us to run forever, and heal almost immediately (scientists are always trying to figure out why fossilized amber has 50% MORE oxygen, the Bible tells them the answers, but II Peter says they are "willingly ignorant"...dumb on purpose), and who knows perhaps man could be 12 feet tall?! In Turkey, they don't want you to know they've uncovered skeletons that are enormously tall, some 12 feet in length, that would make that ark twice as long, twice as high, twice as tall, we use a 6 ft man's cubit of 1 1/2 ft to determine how big we think the ark is, a 12 ft Noah, has a 3 ft cubit?! Also, there is No mention of eating meat till after the flood, I believe it's because that was all there was to eat, grass or meat. PLUS the fear and dread of man on animals came after the flood. Even rain didn't exist before the flood, which is why the rainbow was God's new promise, before that time no rain, equals no rainbow! When the fountains of the deep broke forth, you can bet it was super heated water like in a radiator that turned to steam, steam expands 10,000 to 1, and therefore rises immediately! When the steam ran into our protective ice canopy it started to melt, I believe it took 40 days and 40 nights to completely melt, just a guess ;-)
So the last thing is that we KNOW that Jesus said, "and I saw Satan fall from Heaven to earth like a lightning bolt." How could Satan have fallen to earth if earth was not yet around?
How could God say in Gen 1:31 "it is VERY good." if there was a guy in all red, horns and a pitchfork up to no good already here with a third of the Heavenly hosts?
The adjectives "cunning" or "subtle" describe the serpent tempting Eve, these words are used to describe SPEECH and therefore it's being used to say the snake (as an animal, literally) was a better speaker than the rest of the beasts, in Gen 3:1, nobody even wants to discuss that the animals and man spoke and communicated with each other BEFORE the fall of man.
Keep in mind that God creates everything in 5 1/2 days, then He creates Adam, then Adam watches Him create Eden to the East of him, then God places Adam in the garden and creates one of every beast, cattle and bird to both name and find a help meet, none was found, so God puts Adam to sleep, and creates Eve from a rib of Adam, when Adam awakes he sees her and names her woman...this is EXACTLY what Ch 2 in Gen says, read it.
So Adam witnessed God create the Garden of Eden, and one of each kind of land and air animal out of the dust (birds in ch 1 are created out of air, not in ch 2), and knows but did not witness God create Eve, however, and unfortunately, Eve never saw anything created, she just heard Adam recount his story. It was Adam whom God said not to eat the fruit, and we can conclude by Satan's question, "Hath God truly said?" in ch 3, that Adam had told Eve what God had said. Satan obviously knew Adam had told her 2nd hand, so he used that to create doubt?! See???
I could keep going and going, but I will stop with one last observation, remember that Lucifer was created to "cover" God's full glory to the Heavenly hosts, and Lucifer lead the Angels in corporate worship, this created a unique god-like complex I think, they were facing him, but his back was to God, however when God walked with Adam and Eve in the cool of the day, no Lucifer required, so you can simply do the math! I believe this is the catalyst that caused him to be jealous because of man not having to be filtered through him to worship God!!!
I hope I have helped at least one person here, God Bless ;-)