By technology, 22nd century one would take ~250 years, but since by lore technology is advanced Malta was colonized ~15 years so I think, why Atka failed to terraform.
Primary reason I think is the Gaian terrorists who hate Planetform that they dont want planets to change, it took ~400 years, estimating 100 terrorist attacks that reversed by 4 years, and it was subsequently abandoned because of Gallic invasion. So perhaps this is the cause.
Or Planetform doesnt have enough technology to terraform quickly... its like a slowdown of production.
