It seems the only factor that would determine how long it took to create the earth is how much physical matter restrains it. In other words, if the process was sped up, matter be destroyed? So if a god created everything from nothing, he could create each part right where it was. He wouldn't have to create fire and water and wind and dirt and then use them to form the Earth. He could create each planet, sun and so on already formed in its correct position in the universe, with the exact amount of force required to hold it in place. But maybe a creator likes taking basic elements and forming the universe.