There's actually a way to offset layers inside After Effects but the process is quite tedious. It involves trimming the layers and going to the "Animation" tab then "Keyframe Assistant" and afterwards "Sequence Layer". The problem here is you will end up spending a lot of time trimming and then redoing the process all over again until you get the right amount of gap between the layers. So I wrote my own and I'm giving it to you for free. :)
DOWNLOAD THE SCRIPT
You can download the script for free by simply filling in the boxes below. The direct download link will appear once you press the "Submit" button.
Copy the .jsx file -> Go to Finder -> Applications -> Adobe After Effects CC (Version) -> Scripts -> Paste the script
Copy the .jsx file -> Go to Program Files -> Adobe -> Adobe After Effects CC (Version) -> Support Files -> Scripts -> Paste the script
RUNNING THE SCRIPT INSIDE AFTER EFFECTS
After Effects CC (Version) -> File -> Scripts -> Offset Layers.jsx
USING THE SCRIPT
You can use the script by simply highlighting the layers first that you want to offset, then input the number of frames you want them to move and click "Apply". Start highlighting from the bottom layer towards the top layer if you want the direction to be like a staircase going to the right. On the other hand, if you want the staircase to go to the left start from the top layer and continue on until you reach the bottom layer. That's it!
Do send me a message if you encountered any problems with downloading or running the script: email@example.com. I'm also open to suggestions.