How do I time the appearance of the duplicated images

I am trying to get these attached movie clips to attach themselves in a timed sequential order. One after the next. Any help would be great. I looked all over but didn’t find an answer.

Here is the code I am using:

//////////////////////////////////////////////////////////////// place bg image
var bw = 40;
var sw = Stage.width/bw;
for (i=0; i<sw; i++) {
    var bg = attachMovie("bg", "bg"+i, i);
    bg._x = bw*i;