In 1960, Freeman Dyson proposed how advanced civilizations could create megastructures that enclosed their system, allowing them to harness all of their star's energy and multiplying the habitable space they could occupy. In 2015, the astronomical community was intrigued when the star KIC 8462852 (aka Tabby's Star) began to dim inexplicably. While an analysis of the star's light curve in 2018 revealed that the dimming pattern was more characteristic of dust than a solid structure, Tabby's Star focused attention on the concept of megastructures and their associated technosignatures.
And the worst part would be that if you fuck up the math some of the existing planet might get plunged into the sun or out of the star system if new planet is introduced or existing one is moved. As I understand it the predictions for the state of orbital system even now are only so good for certain amount of time before they become inaccurate and chaotic.
The time frame from stable orbit to any sort of habitability must be tens of thousands to millions of years. Probably massive floods from melting ice are the minimum if talking about a frozen snowball and atmosphere raining down if the deal is about cooling some Venus clone.