[Alneyan]

500 turns after having built that Atmosphere Converter, the planet was still a gas planet. The only way to change its type would be to destroy the planet and recreate it.

Slick, the standard delay to build an Atmosphere Converter will likely be 5 turns, and not 8: Emergency Building does wonder in such situations. All slots will likely be filled already, or you will build facilities taking a single turn to build, so Emergency Building will not really hurt you (unless you have a spaceyard there and want to build ships while the conversion goes on). Otherwise, I fully agree with your analysis.