The Facebook timeline is dictated by a set of algorithms used to   asses how interested an individual FB account user is with a posted story.

This is based on three steps of logic:

• Inventory: Stories you have not seen from your friends and the pages that you follow.
• Signals: Information FB has available to make informed decisions about your likes such as:
  • Age of post
  • Who posted the story
  • How fast is your internet speed when accessed
  • Type of phone or electronic device you are using
  • What kind of content may be problematic to you
    • Spam
    • Click Bait
    • False News
  • Predictions: FB determines how likely you are to comment, share, hide or report each story.

Facebook collects a few dozen predictions then weight them.  After, they roll them up into a relevancy score and present posts to your timeline based on those scores.

The stories in your newsfeed are likely to by chronological because the age of a story is one of the determining signals.  However, it is not strictly so.