How to Create This Timeline Effect - Workflow

That exact look will be easiest to pull off if you set up 3D layers in After Effects and offset the layers in Z space. If all of the layers are tied to the movement to a null, the layers closer to the camera will move faster than those farther away. They have offset the start and stop a little, which could be accomplished by adding a couple of keyframes to the lower layers.

The animated timeline could be a single wide Illustrator file with some effects. Again, this would be a 3D layer. 

The hardest part of this type of timeline animation is creating the original artwork and planning the animation. You also want to figure out where you can make some invisible cuts. You would not want a single five or ten-minute comp because it gets hard to manage. 

The last time I created something like that, I designed a moving background after I had animated all of the layers as shots that could be cut together without any visible edits. Most shots moved in and out of the frame at about the same speed. The more detail in the shot, the longer it stayed basically still. All the shots (comps) were rendered with a transparent background and edited in Adobe Premiere. Another render with an alpha channel was rendered, which was brought into After Effects so that I  could add the moving timeline bar and any additional text. 

Almost every photo in your sample had an animated reveal. I. would create a separate comp for each of those reveals and probably render them. The trick to working efficiently is to separate each moving element into its most basic form, then either pre-compose the part to be animated or make it a separate comp and render it.

I have found that the most efficient workflow starts with sketching out a rough storyboard with pencil and paper. I then take pictures of the sketches with my phone, add them to a Premiere Pro sequence, and cut them to a scratch audio track. That gives me a rough idea of how the timing will work and lets me know if I have enough time for the audience to understand the story I am trying to tell.

I watched your sample movie three times. This is how I would break down the project: A whole day to collect and organize photos and prepare sample art. Another day to prepare storyboard ideas, plan,  and record a sample audio track. Another day to create the animated reveals for the 20 stills. Then one more day for the text and graphics and the first assembly. Then I always let projects like this sit in a special Marinate folder for a day unless I'm under a deadline to make sure that the story works. I always walk away for at least an hour before finalizing an edit. If I did well on the first cut, it usually only takes another couple of hours to fix things up and do the final render. There you go. That short video probably represents about a week of somebody's hard work.

I hope this helps.

Let us know if you have questions about specific things like the photo reveals or the animated line.