this is the file:
https://github.com/discourse/discourse/blob/master/app/models/top_topic.rb#L143-L192
there were topics about top-page algorithm, but i couldn’t re-find them using the search.
i don’t think that’s how it works, since not all the latest topics are shown in the top page. there exist some score and the topic should get the minimal score to be shown in the top page.
and you can change the top-scoring parameters in the admin setting panel, in the developer tab.