Requested feature overview description.
Popular by Year & All Time filters
Simply put, adding to the popular page of the site a "year" filter allowing popular by year, and then an "all time" button to sort out whats been the most popular on the site in all time.

By year, might look something like this;
https://e621.net/post/popular_by_year?year=2017
While all time, might look like this;
https://e621.net/post/popular_all_time?amount=32
Allowing users to type in an amount in the URL bar to show how many they want to see. Possibly maxed at some amount, if you prefer.

Why would it be useful?
Well, popular by day is pretty useless, its not like you have that many people upvoting things every single day. Week is a little better on the statistics but, still not that great. Month is good because it gives time for an image to be examined by many more. However, I think for the best stats of what is most popular, a per year and an all time filter would show the best results.

What part(s) of the site page(s) are affected?
post, I think. "e621.net/post/popular_by_day"
Adding "popular_by_year" and "popular_all_time"
Altering "popular_by_day" "popular_by_week" "popular_by_month"