couple things going on here.
first, this pretty much is a far-after-the-game-crashes kind of target, barring aggressive use of SM mode, and if you're using SM mode, you can edit a planet to habitability in zero days. or, you know, edit the Roach People from Hell who can live anywhere.
that said, max tech is . 008 atmospheres per year per module (or installation). how much atmosphere you need to add (or remove!) depends on the planet. The magic number is . 3334 ATM- a good colony site (such as Mars) has a temperature close to tolerable, and you can add . 1 ATM of oxygen and . 2224 ATM of nitrogen/ greenhouse/ anti-greenhouse as needed to make the temp OK and have a 0. 0 colony cost when you're done.
. 3334 atmospheres in one 5 day tick would take . 3334/ (. 008/72) = 3001 modules, ignoring the effects of leaders. the "72" is the conversion factor, 72 5-day ticks per year. I dont know that even SM mode can get you a naval officer with more than . 3 terraforming bonus, which would bring you down to merely 2309 terraforming modules. with installations in theory you can have a governor bonus of . 65 and a sector bonus of . 15625, cutting your requirement to 1574. but you need the pop to run the installations and AFAIK SM powers cant get you admins this good.
Meh, just SM a billion people on venus. put enough ground troops there to make them quit their whining and periodically edit their numbers back up to a billion. what's the point of being God if you're going to be a pantywaist about it?