Any other explanation of creation is heretical. The plain reason is that the Bible itself knows no other version, acknowledges no other version, and bases its entire theology and history upon it. Without an historical six day creation the rest of the Bible falls, having been deprived of its reason to exist.
All of the teaching of the Bible is based upon its own version of history, and apart from that history its teaching is meaningless. Thus we see the closest link between sacred history and sacred theology. One cannot exist without the other. Nothing could be simpler.