In reality, it took far, far longer than seven days to create the universe as we know it today. A great deal of well-founded scientific research concludes that our universe was "born" about 13.7 billion years ago in a massive expansion that blew space up like a gigantic balloon. In very simplistic terms, that is the Big Bang theory, which virtually all cosmologists and theoretical physicists endorse. The evidence that supports the idea is extensive and convincing. For example, scientists and physicists know that the universe is still expanding even now.
Scientists have also discovered a predicted thermal imprint of the Big Bang, which is the universe-pervading cosmic microwave background radiation. They have not been able to positively identify objects older than 13.7 billion years. "All of these things put the Big Bang on an extremely solid foundation," said astrophysicist Alex Filippenko of the University of California, Berkeley. "The Big Bang is an enormously successful theory." Traditional Big Bang theory presents the idea that our universe began with a singularity — a point of infinite density and temperature whose nature is difficult for our minds to grasp. 
Even though the very rudimentary beginnings of the universe remain somewhat unclear in scientific terms, researchers believe they can pick the story up at about the time immediately after the Big Bang occurred. At that point, they believe the universe underwent an extremely brief and dramatic period of inflation or growth, expanding faster than the speed of light. It doubled in size perhaps 100 times or more, all within the span of a few tiny fractions of a second. "Inflation was the 'bang' of the Big Bang," Filippenko told SPACE.com "Before inflation, there was just a little bit of stuff, quite possibly, expanding just a little bit. We needed something like inflation to make the universe big."
The question of what preceded the Big Bang is even more mysterious and hard to tackle. Some scientists theorize that empty space, with only a relatively small amount of matter, existed before the Big Bang occurred. This seems to be an idea that the Bible supports.
If you closely examine each individual verse in Genesis chapter 1, which recounts the earth’s creation, you can begin to grasp how complex the entire process was. True science and the Bible go hand in hand and are not contradictory to each other if you consider that Almighty Jehovah God possessed all wisdom and power and created the very laws of physics and natural science that mankind tries so hard to discover.
On the first day of creation, Genesis 1:1-5 says that in the beginning God created the heaven and the earth, but the earth was void of form, covered by water. It was dark, but He also created light on the first day, thus also was the formation of Day and Night. But note that this light was not the sun, moon, or stars, because that part of creation did not come in to existence until the fourth day, or quite likely, the time during which the Big Bang happened (Genesis 1:14-19).
The creation of the heaven and earth was remarkable indeed, and evidence proves that each “day” likely lasted thousands, if not millions of years. On Day 2, Jehovah separated the waters that that covered the earth into a firmament above the earth, making the atmosphere that safely envelopes our planet in (Genesis 1:6-8).
The third day was an extremely long one, for it was during that time that dry land (called Earth) appeared out of the waters, and the gathering of the waters were called Seas (Genesis 1:9-10). One can only imagine how great an expanse of time elapsed while the earth was shifted about, with mountains, valleys, plains, and hills appearing. What a massive upheaval and change the earth must have seen! If you’ve ever visited the Grand Canyon in Arizona or traveled to any mountainous locale, you have no doubt seen the many layers of sediment and how they were compressed and convoluted through time in amazing ways.
The natural forces of wind, ice, water, earthquakes, volcanoes, and other phenomena were definitely at work in the early phases of Day 3, but that was only a part of it! The third day also brought plant life and vegetation to the earth. And again, for every tree, plant, or vegetable that Jehovah created, consider the thought and planning that went into each individual species and how long it would have taken for each variety to mature and re-seed itself until the earth was covered with greenery (Genesis 1:10-13).
As we briefly touched upon, the 4th day brought what is likely the “Big Bang”, or the time when the universe vastly expanded. Here is where the sun, moon, and stars were made. If you have ever looked up into the sky on a dark night, away from city lights, you can see myriads of stars that seem as if they go on forever in outer space. Jehovah said these particular lights would be for “signs, seasons, days, and years". Think how the sun affects the seasons during the earth's rotations and the effect that the moon has on the ocean tides (Genesis 1:14-19).
On Day 5, the sea creatures and winged fowls were made, each after their own kind (Genesis 1:20-23). According to the marine census database, there are well over 15,000 species of saltwater fish alone, not to mention the vast array of other aquatic creatures there are! The number and variety of birds throughout all temperate zones worldwide is mind-boggling as well, from tiny hummingbirds to penguins, ostriches, and everything in between! Jehovah caused all these species, both marine life and fowl, to multiply during this "day".
Genesis 1:24-25 explains the creation of all the land animals that inhabited the earth on Day 6. What a lot of imagination and ingenuity Almighty God must have put into this part of the creation, mixed in with a bit of humor, too! Look at an aardvark, elephant, or platypus and you would likely agree! The variation in each animal, the area they inhabit, their diet, instincts, and characteristics are all so unique! It seems very plausible that the dinosaurs, woolly mammoths, and other now extinct animals might have also lived during the early part of this “day” as their bones or fossilized remains give evidence that they indeed roamed the earth at some point in time.
Day 6 also brought about the creation of mankind (Genesis 1:26-28). Note verse 26 where it says, “Let us make man in our image.” The “us” no doubt refers to Jehovah’s Son who was created even before anything else came into being. Proverbs 8:22-31 provides strong evidence of this point and how the two of them created everything else together.
In conclusion, true science agrees with Bible teachings. The “week” (actually 6 “days”) of creation took millions of years to come to fruition. What an amazing Master Planner, Artist, and Physicist our Creator is to have made the universe what it is, along with His beloved Son! No wonder He was ready to rest from creating on the seventh day! (Genesis 2:1-3)
“And God saw everything that he had made, and, behold, it was very good...” (Genesis 1:31)