1 second backwards and one posted a picture and the other did not. The timestamps are derived from the moment you press reply. If you are uploading a picture @:56 and someone is not at :57 then the :57 will post first.
Again, with a picture vs without. Show one where a single non-picture post was backdated 8-14 seconds, and then for a bonus make sure it has a zero delta with PDJT.