How long will it take for the sun to become a Red Giant?

It will most likely happen when the earth is free from all life forms. While the sun is very slowly dying, it must be getting weaker. This will change all things on earth from the weather, plant growth and other such things. And eventually, we will all die. Whether that means all the land will be drowned or dried, it makes no difference. One way or the other our planet will meet its fate. Even if we did survive the earths changes, we won't survive when the sun causes our whole existence to burn to nothing. We would all be dead before we even knew what was happening because of the heat closing in on us. Kind of the reverse of what they call "The Big Bang".