You have quite a few elements & timelines on your project. But as far as I can tell You are not understanding how timelines work. I am going to focus on the (17) text elements all named “Text 12”. In any of the six timelines I am not seeing anything happening except at time “0” where some of the timelines have the same “Text 12” element with its “Display” property set to “Hidden”.
However, the “Main Timeline” has all (17) of the “Text 12” elements “Visible” at time “0” which is why You are seeing them all at once - even though some of the other timelines have various “Text 12” elements set to “Hidden”.
There was a post along these lines recently, with responses by @MarkHunte & @jonathan that might illuminate for You the way timelines work.
BTW: Would be great to see this project when You are finished - I think the “Battle of Britain” is a fascinating topic.