I'm currently debating with someone about Naruto's stamina in the war and I'm trying to zero down specifically how long Naruto ACTIVELY fought in the war in a single go. I'm talking his longest stamina feat without being given further Chakra by some external source.

I've googled stuff at it just goes over how the war lasted 3 days. I know that Naruto entered the war on the 2nd day, but he was admittedly on the sidelines for quite some time.

After reanimated Madara entered the battle and the 5 kages took over, the clone that was fighting there returned to Naruto's majn body if memory serves correctly. He then had some recoup time.

Then that night were the fights with Obito and Madara until he was almost killed and Gaara had to evac him. He was then fully recovered with Hagaromo's Chakra. This happened during the early morning of the 3rd day

Then a bunch of battles happened with other characters that Naruto wasn't a part of.

Infinite Tsukuyomi was cast and a lot of stalling occured.

Then the final battle vs Madara until Kaguya took over- maybe minutes.

I read that the battle vs Kaguya took place within about 40 minutes. Lots of stalling and planning in that battle.

After Kaguya got sealed, the 3rd and final night was over. Naruto and Sasuke started their battle at the Final Valley the next morning during sunrise. They battled until the sun was setting. They were then found by Sakura and Kakashi that night.

IN CONCLUSION Naruto's largest stamina feat was during his battle with Sasuke and he was being fed a BUNCH of extra Chakra from Kurama. Roughly 10ish hours of fighting fueled by external sources.