The six-day creation account has caused a lot of controversy, and especially in later years in the face of higher criticism, methodological naturalism and the theory of (macro)evolution.
The orthodox Lutheran, and I would argue the historical Christian, position, is that six days means simply 6 natural 24 hour days. This is what Luther taught and is affirmed by several, if not the vast majority, of heavyweight Lutheran theologians since.
This position is still held by the WELS, and though the LCMS have been somewhat vague on the subject of late (though they didn't used to be!), in 2019, they re-affirmed an official stance on it where they absolutely affirm that the world was made in six natural days.
So, this is all to say, the historical orthodox Lutheran position is that six days means just that - six days. Now, I don't think other views are necessarily considered heresy, but heterodox.
As a side note, I can add that I wasn't raised a Lutheran - I come from a Pentecostal/Charismatic/non-denominational environment, where I just took for granted that the six-day creation account was figurative, for that's essentially what the world and my church bodies taught. I went from being a firm believer in that the creation happened over millions of years, to being indifferent, to then finally realising that we're not at liberty to stretch the meaning of God's Word. I'll explain:
Scriptures clearly teach that:
1. All of Scripture is God-breathed and true.
2. Our Lord Jesus Christ, who is God in flesh, refers to the creation account as true, and this is reflected throughout the NT. In other words, we have the sure testimony of Jesus, who, as God, created the world.
3. Adam was the first man, created out of the earth directly by the hand of God. This is contrasted by Eve, who was created by God out of Adam. It is very clear that they were not born of natural birth, but created. It is also very clear that they were not made from animals, but were made in the image of God as an entirely different species.
4. There was no death before the fall. Death, both temporal (separation of body and spirit) and eternal (damnation), are consequences of sin, and were not part of God's original creation. We also see this original design echoed in the new creation, where once again, we are (1) raised bodily and (2) are never to die.
This is just a brief summary, and there are many other arguments that can be made, but I think these are perhaps the most important ones that clearly illustrates how incompatible the theory of evolution is with Genesis.
Basically, Genesis is not a poetry book, and we can't force modern theories on it, but it needs to be read and understood on its own terms, because it sets the foundation for the other books of Moses and ultimately all of Scripture, which centres around and culminates in the person and works of Christ. For example, I think it can be easy for someone who views Genesis as a purely figurative work to lose sight of the creation with original righteousness, then the fall and original sin, which then produces a low view on sin and God's Law, which then reduces the Gospel.
When it comes to creation controversies, I think the best position we can take is, rather to speculate on theories that can work, is to be on guard against theories that do not work and be content with what God has revealed. The creation was undoubtedly of epic proportions, yet, in the Bible condensed to only a few words, where it quickly shifts focus to man: the crown of God's creation, and Jesus Christ, the Lord of all.
