They could travel to the past and accidentally change something that has a huge impact on the present. For example, Naruto might prevent an event that was crucial for the development of a certain jutsu. This would then lead to a series of challenges as they try to fix the timeline.
Another idea is that they time - travel to a time when a great evil was about to be unleashed. Team 7 has to work together with the shinobi of that era to stop it. Sasuke could use his Sharingan to understand the enemy's motives, Naruto would be the driving force of hope, and Sakura would heal the wounded. They'd also learn a lot about the history of ninja clans in the process.
One idea could be that Team Konohamaru travels back to the time of the First Hokage. They could witness the founding of Konoha and get involved in some of the early battles against rival clans. Maybe they help Hashirama in some way and learn valuable lessons about leadership and unity from him.
In a team Iron Man time travel fanfiction, a great plot could be that Iron Man travels to the future by accident. There, he discovers a world in ruins because of some actions he took in his present. So, he has to travel back and correct those actions. He teams up with his past self and other Avengers from different time periods to make sure the future is saved. This would involve a lot of character development as the different versions of Iron Man and the Avengers have to work together and understand each other's perspectives.
Maybe they time travel to a point where a major battle was lost in the past. Kakashi and Team 7 could change the outcome of that battle. For example, if they go back to the battle against the Nine - Tailed Fox when it first attacked Konoha. They might be able to prevent some of the destruction and save more lives. Or they could travel to a time when a powerful ninja was wrongly exiled, and they work to clear that ninja's name and change the course of history.
Perhaps they travel to a time in the past where a powerful and dangerous jutsu was first created. They have to stop the jutsu from being misused in the future. Along the way, they face challenges like dealing with the original creator who might not want to give up on his creation, and also face other ninja who want to steal the jutsu for their own evil purposes.
One interesting plot twist is if they time travel and find that the world they end up in has a different version of the Chakra system. They have to adapt quickly to this new form of energy while also trying to find a way back home. Also, imagine if they time travel and discover that Naruto was supposed to be born in a different village in this alternate timeline. This would completely change the way they view Naruto's destiny and their role in protecting him.
One idea could be that Naruto travels back in time and gets adopted by a different clan. For example, the Uchiha clan. This would change his whole upbringing and how he views the world. He might learn different jutsus earlier and have a different relationship with Sasuke.
A cool plot idea could be Minato traveling back to his own childhood. He could then use his future knowledge to train himself more effectively, making himself an even more powerful shinobi at a younger age. This would have a huge impact on the future of the Leaf Village as he would be able to better protect it earlier. He might also be able to prevent some of the early tragedies that happened in the village.
One idea could be Tobirama traveling to the future and seeing how his village has developed. He might be shocked by the new technology and the different ninja techniques. Another plot could involve Tobirama going back in time to change a crucial event in Naruto's past, like preventing the Uchiha massacre. Or perhaps he travels to a different timeline altogether and has to find a way back while dealing with that timeline's unique challenges.
One idea could be Naruto traveling back in time and meeting Hashirama. He could learn about the founding of the village directly from Hashirama. Maybe Naruto helps Hashirama deal with some early threats to the village that were not well - documented in history.
One interesting plot idea could be Kakashi traveling back in time to before the Uchiha massacre. He could try to prevent it, which would completely change the future of the Naruto world. Maybe he'd have to face off against Danzo and his schemes early on.