My question is at approximately what point in time did the English language evolve to a form that the advantage person today would be able to have a basic conversation with a common person from that time
Here's a couple from here that might be what you're looking for:
/u/Lewed_Lose and /u/Steakpiegravy answered in this thread https://www.reddit.com/r/AskHistorians/comments/8azxei/i_can_partially_understand_middle_english/
and
I found these threads over in /r/history with some more information, although I have no idea as to the accuracy of them, or any of them really.
https://www.reddit.com/r/history/comments/320in5/linguists_of_reddit_how_far_back_in_history_could/
https://www.reddit.com/r/history/comments/4mfz9n/how_far_back_in_time_would_an_english_speaking/
And one from /r/lingusitics
https://www.reddit.com/r/linguistics/comments/1b5qez/how_far_back_could_i_speak_english_and_be/
And a couple others with more information.
https://www.reddit.com/r/AskEurope/comments/7wkwzs/how_far_can_you_go_in_history_and_still/
https://www.reddit.com/r/videos/comments/87g2v0/old_english_is_an_entirely_different_language_a/
Hopefully this will tide you over until someone with actual knowledge of this can help you out!
Here’s a fun thing: look at Shakespeare’s Love’s Labor’s Lost Act 4 Scene 1. The characters complain about how another character speaks. The scene marks the moment that modern pronunciations were coming into existence.