Browsing a few articles and books online supports the idea that most church fathers supported neither a 7-day creation nor an indefinite one, but rather a creation of 7-10,000 years (arguing from the verse that 1,000 years to God is but a day). This supports my assertion that the Genesis account was not generally taken literally.
“There is, unfortunately, a common misconception that Christians all used to take it [Creation] fairly literally, and that in a post-Copernican and Darwinian age some of us are now trying to cobble together some kind of non-literal understanding. This is simply not true. At no stage in the history of Christian interpretation of Genesis 1 – 3 has there been a ‘purely literal’ understanding.” - Roger Forster and Paul Marston, Reason, Science and Faith, p.198, Monarch Books © 1999
“And how could creation take place in time, seeing time was born along with things which exist? . . . That, then, we may be taught that the world was originated and not suppose that God made it in time, prophecy adds: ‘This is the book of the generation, also of the things in them, when they were created in the day that God made heaven and earth’ [Gen. 2:4]. For the expression ‘when they were created’ intimates an indefinite and dateless production.” (Clement of Alexandria, Miscellanies 6:16 [A.D. 208]).
“For who that has understanding will suppose that the first and second and third day existed without a sun and moon and stars and that the first day was, as it were, also without a sky? . . . I do not suppose that anyone doubts that these things figuratively indicate certain mysteries, the history having taken place in appearance and not literally” (Origen, The Fundamental Doctrines 4:1:16 [A.D. 225]).
“And with regard to the creation of the light upon the first day . . . and of the [great] lights and stars upon the fourth . . . we have treated to the best of our ability in our notes upon Genesis, as well as in the foregoing pages, when we found fault with those who, taking the words in their apparent signification, said that the time of six days was occupied in the creation of the world.” (Origen, Against Celsius, 6:60).
For what it’s worth, a reasonably scholarly series of articles on what the early church fathers said about Genesis begins here.