I have a long term project to add Timelines to Wikipedia
All Timelines listed under my name on Commons were created by me. They are a bold way of immediately capturing a users attention and showing the general flow of events.
Dates are salient, or important, when the text of the Wikipedia article seems to think so. It is not possible, for example, to capture EVERY battle of the 100 years war. But the Battle of Agincourt has got to be in there. Bias is possible in selecting salient dates. Just email me if I've made a bad call, and I can correct.
None of my timelines shown on Wikipedia intentionally include original research.
Other timelines found on my own website Imsaho.com, may be of interest to you.