One plot idea could be Naruto using his newfound time - stopping ability to prevent a major disaster in Konoha. For example, he could stop time just as a powerful enemy's ultimate attack is about to hit the village, and then find a way to counter it while time is frozen. Another idea is that Naruto uses it to have some peaceful moments with his friends and family that are always cut short in the normal flow of time. He could share a meal with his dad, Minato, and have a long conversation that was never possible before.
One idea could be Naruto going into the time chamber to train for a new, extremely powerful jutsu that no one has ever seen before. He could emerge with this jutsu and use it to defeat a powerful, new enemy that threatens the Hidden Leaf Village.
A really interesting plot would be if the male OC's time - stopping power has a limit. He discovers that every time he uses it, it drains his energy and he has to find ways to replenish it. This could lead to him having to make difficult choices about when and how often to use his power. Maybe he has to form an alliance with a magical being that can help him manage his power in exchange for some favors. And all this while, he's also dealing with the normal high school drama in the DxD universe like dealing with rivalries and making friends.
Perhaps Naruto time - travels and ends up in a world where he is a baby again but with all his current powers and knowledge. He has to figure out how to use his abilities at such a young age without revealing too much. This could lead to some really comical and heartwarming moments as he interacts with the people around his baby self.
One idea could be that Naruto and Sarada travel back to the time of the founding of Konoha. They could witness the first Hokage's decisions and how the village was initially built. This would give Sarada a new perspective on the history and values of the village.
A plot could involve Naruto and Sasuke being stuck in a time loop where they are the only ones aware of it. Each loop, they find that small changes in their actions lead to big differences in the outcome. For example, in one loop, if Naruto decides to train differently, it changes how Sasuke views their rivalry. They could be trying to break the loop by fulfilling a certain prophecy or task that they gradually uncover.
One idea could be Naruto using the hyperbolic time chamber to train intensively for a new and extremely powerful jutsu. He could emerge with a whole new set of skills that surprise his friends and foes alike.
One interesting plot could be the main character going back in time and using modern knowledge to change the outcome of some key battles in the Naruto universe. For example, they could introduce new jutsu combinations or strategies.
Maybe baby Naruto time travels to a time when the Uchiha clan was still thriving. He could interact with the young Sasuke's family and somehow change the course of events that led to the Uchiha massacre. This would create a whole new timeline with different challenges and relationships.
A possible plot could be that the genderswapped Naruto time - travels to the time of the Third Ninja War. She could use her skills and knowledge from the future to help the younger versions of her friends and comrades. She might also have a different approach to the war, perhaps trying to find diplomatic solutions instead of just relying on combat, due to her different perspective as a genderswapped character.
One interesting plot idea could be that Naruto travels back in time and meets Kakashi when he was younger. Naruto could use his knowledge of the future to help Kakashi in some way, like preventing a tragic event from his past. Another idea is that Naruto and Kakashi are sent back in time together and they have to work together to change the future of the ninja world. They might have to face old enemies in new ways.