"The further out the orbit the slower the assembly time of the planets, I'd suspect."

Even if so we have ample evidence of planetary formation at several AU. An early F star at 4-6 sols luminosity would have a wide liquid water HZ. We could seed any newly formed reduction atmosphere Earths with oceans with Earth-style algae and jump start O2 formation. Next, add land plants and Viola! a habitable planet or three for nice run of a hundred million years more or less. Yah, minor technical problems like shielding from excess UV B. Left as an exercize for the 4th millenium grad student.