Ideally, atheists would like to imagine that the universe has always existed. Aristotle believed in a Universe existing unchanged throughout eternity. Millennia later, as monotheism waned, this idea became popular again. In the early 20th century the common worldview held that the universe is static — more or less the same throughout eternity. No creator needed.
Furthermore, atheists would like to imagine that life has gradually developed. Obviously, for a complex machine such as a living thing to pop into existence suddenly would require an intelligent designer - or, in other words, God. However a very, slow gradual process conceivably could be natural and spontaneous. Therefore Darwin wrote:
As natural selection acts solely by accumulating slight, successive, favourable variations, it can produce no great or sudden modifications; it can act only by short and slow steps. Hence, the canon of "Natura non facit saltum," [meaning "nature does not make jumps"] which every fresh addition to our knowledge tends to confirm, is on this theory intelligible. (Origin of Species Chapter 14: Recapitulation and Conclusion)
About 200 million years ago, there was a sudden transition from smaller reptiles to giant dinosaurs. Here is a photo of the Triassic-Jurassic boundary.
About 65 million years ago, there was a sudden transition from dinosaurs to mammals. Here is a photo of the Cretaceous–Paleogene boundary.
For Judaism, however, as I have explained, I don't think this is a problem.