I'm not sure I explained things very clear :/ In fact actual timelines are related to their maps. Timeline 1 is history of events past in the time of map 1. They just cause changes that you can further see then on the map 2. But timeline 2 talks about the events of the second age (map2). By the ways maybe this idea was a bit confused to work on the map or a bit too complicated, so the idea from SK is probably the easiest to set up without breaking the all map design and look (which I actually like ).
Well, thanks Chasio, SK and Vorro for your time and your suggestions about that, it's much appreciated. And don't worry Chasio, if it were hanging on your wall, you'd see it's not that big so no need for a stepladder!