Quoting myself again, with just a few examples...
Ephraim the Syrian on the First Day: "Although both the light and the clouds were created in the twinkling of an eye, still both the day and the night of the First Day continued for twelve hours each."
Basil's Hexaemeron says that before the third day of creation, there was nо natural necessity for waters to flow downward until God's command came. He also emphasizes the instantaneous nature of God's creation. For example, on the Third Day: "At this saying all the dense woods appeared; all the trees shot up.... Likewise, all the shrubs were immediately thick with leaf and bushy; and the so-called garland plants ... all came into existence in a moment of time, although they were not previously upon the earth."
Most Patristic authors embraced the instantaneous nature of creation.
Ambrose: When Moses says "In the beginning God created," he intends to "express the incomprehensible speed of the work." ... "He (Moses) did not look forward to a late and leisurely creation of the world out of a concourse of atoms." (Against Greek cosmology.)
Athanasius: "As to the separate stars or the great lights, not this appeared first, and that second, but in one day and by the same command, they were all called into being. And such was the original formation of the quadrupeds, and of birds, and fishes, and cattle, and plants.... No one creature was made before another, but all things originate subsisted at once together upon one and the same command."
Ephraim describes the activity of the Spirit on the First Day: "[The Holy Spirit] warmed the waters and made them fertile and capable of birth, like a bird when it sits with its outstretched wings on its eggs and by its warmth gives them warmth and produces fertility in them." Regarding the Third Day, Ephraim says, "The herbs, at the time of their creation, were the productions of a single instant, but in appearance they appeared the productions of months. Likewise the trees, at the time of their creation, were the productions of a single day, but in their perfection and fruits, which weighed down the branches, they appeared the productions of years."
Plants and trees appeared on earth, the Fathers repeatedly agree, before the very existence of the sun.
Chrysostom: "(Moses) shows you that everything was accomplished before the creation of the sun, so that you might ascribe the ripening of the fruits not to it, but to the Creator of the universe."
Basil: "The adornment of the earth is older than the sun, that those who have been misled may cease worshipping the sun as the origin of life."
Ambrose: "Before the light of the sun shall appear, let the green herb be born, let its light be prior to that of the sun. Let the earth germinate before it receives the fostering care of the sun, lest there be an occasion for human error to grow. Let everyone be informed that the sun is not the author of vegetation.. . . How can the sun give the faculty of life-growing plants, when these have already been brought forth by the life-giving creative power of God before the sun entered into such a life as this? The sun is younger than the green shoot, younger than the green plant."
Basil teaches that the "kinds" of Genesis are fixed to the end of time: "The nature of existing objects, set in motion by one command, passes through creation without change, by generation and destruction, preserving the succession of the kinds through resemblance, until it reaches the very end. It begets a horse as the successor of a horse, a lion of a lion, and an eagle of an eagle; and it continues to preserve each of the animals by uninterrupted successions until the consummation of the universe. No length of time causes the specific characteristics of the animals to be corrupted or extinct..."
Ambrose is even able to fix the month of the creation of heaven and earth using Scripture: "He created heaven and earth at the time when the months began, from which time it is fitting that the world took its rise. Then there was the mild temperature of spring, a season suitable for all things. Consequently, the year, too, has the stamp of a world coming to birth.... In order to show that the creation of the world took place in the spring, Scripture says: "This month shall be to you the beginning of months, it is for you the first in the months of the year" (Ex. 12:2), calling the first month the springtime. It was fitting that the beginning of the year be the beginning of generation."