We should be dropping bags of extremophile organisms into the Martian atmosphere to get a start on terraforming it.
The best time to start terraforming a planet is 500 years ago. The second best time is now.
The best time to start terraforming a planet is never. The idea is as absurd as a Dyson sphere/swarm. People should really grow beyond sci-fi ideas that were last fresh in the 1930's.