After reading this Question and the ingenious answer from Dimitri mx (kudos) and a related comment, I came to wonder how One Piece would compare.
The anime was launched in October 1999 and is still ongoing.
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Before I start with the actual comparison, I would first like to note that in the current point in time, Naruto and One piece do not differ to much in run time. But taking into account that Naruto is running towards the end, and Oda Eiichiro said that he is about the half way mark, we can safely assume that in a near future this will change. With that said.
Just like in my mentioned answer, I have been using Myanimelist as a source of times. And came to the conclusion that it would take you
18945 Minutes of non stop watching one piece (excluding cross-overs)
which equals to 315.8 Hours or 13.2 Days
making the difference in time about 1620 Minutes
which equals to 27 Hours or slightly more then 1 day
This difference in run time is caused by One piece having:
Where as Naruto only beats one piece in
One Piece 710 episodes (currently), roughly 24 minute's/Episode*
~17040 Minutes or 11.8 days
All tough most of the ones listed under this tab are officially known as specials, I still decided to list them in their own sub-category of movies as I found it to be more fitting.
Small side note: All tough I taught it was said for Naruto fans to wait a whole week, One piece fans had a even harder time having to wait 832 weeks or 16 years! With the sole exception being Hinati Fujinamai Ending revealed to severely sick boy
JapNation AniManga reports that Eiichiro Oda was glad to tell the kid how One Piece ends and that he was holding back his tears upon seeing the condition of Hinati Fujinami. While Oda was fine with Hinati Fujinami learning about the One Piece ending, Oda requested to talk to the child alone so that details about the One Piece manga ending wouldn't be leaked while he jokingly pleaded to Hinati to not reveal it to the press. JanNation AniManga noted that at the end of their talk, Hinati Fujinami was reportedly seen smiling but crying at the same time as he told the people that One Piece is "beautiful".