That way, you'll have more time to research tech and unlock new stuff to give you a better chance as the end draws nigh. Guerrilla Ops assignments can also provide a significant delay.
As the bar reaches its halfway point, complete Alien Facility missions to drop it by at least two points. However, you can delay things quite a bit. Once the Avatar project is completed, you'll be in a world of hurt if you're not prepared. The Advanced Warfare Chamber Is Terrific.Scientists, Engineers, and Intel Are Your Friends.