Ban could be another one. He has his own backstory related to the sins and his immortality. He might time travel to find a way to break free from his immortality curse or to go back and correct a mistake he made when he was under the influence of one of the sins, like greed when he stole something important in the past.
In some fanfictions, the time travel could be used to bring back a character who was lost due to one of the seven deadly sins. For example, if a character was killed because of envy among the group, another character might travel through time to stop that envy from taking root. This could lead to a whole new set of relationships and adventures within the 'Seven Deadly Sins' universe.
Star - Lord is a likely candidate. He's always been a bit of a risk - taker and his curiosity might lead him to experiment with time travel technology.
I think Fundy would be likely to time travel. He has a complex relationship with his family and the SMP. Time travel could be a means for him to understand his father better or change the way his family relationships developed. GeorgeNotFound could also be a candidate. He's often in the background but has a strong connection to Dream. Time travel might be his way of getting more involved in the SMP's events and helping Dream in a different way. Lastly, Niki could be a time traveler. She has been through a lot of changes on the SMP, and time travel could be her opportunity to go back and make the SMP a more inclusive and friendly place from the start, especially for those who have been marginalized.
I think Tyrion Lannister would be an interesting character to time travel in a fanfiction. He's very intelligent and cunning. Time travel could be his way to outwit his family and those who have wronged him. Arya Stark could also be a likely character. She has the skills of a faceless man. If she could time travel, she could use her skills to change the past, perhaps by assassinating key enemies before they cause harm. And of course, Melisandre. She has some sort of magic related to seeing the future. It's not a stretch to think she could find a way to time travel in a fanfiction and change the course of events in Westeros.
Lelouch is a very likely candidate. Given his intelligence and his desire to change the world, time travel could be a means for him to correct past mistakes or gain more power to overthrow Britannia. Another one could be Suzaku. He has a strong sense of justice and might use time travel to prevent some of the tragedies that occurred.
Obviously, Natsu would be one of the main characters. And from the Seven Deadly Sins, Meliodas is very likely to be a main character as well since he's the leader.
Hermione is also a prime candidate. Her inquisitive nature and her thirst for knowledge could lead her to accidentally stumble upon a time - traveling mechanism. Once in the past, she could use her intelligence to interact with historical figures and gain new insights into magic that she could bring back to the present.
Morgana might also be involved. If she were to travel through time, she could either try to change the past to gain more power in the present or she could be sent to the future to see the consequences of her actions. This might lead to a change of heart for her, or it could make her more determined to achieve her goals depending on what she witnesses.
I think Yamato could be a good choice too. His ability to control wood style could be really useful in the past. Maybe he could time - travel to help with the growth of the first trees in the ninja world or something like that. And his calm and collected nature would help him adapt to the new situation in the past.
Izuku Midoriya is a likely candidate. His strong sense of justice and his journey to become the greatest hero make him a prime character for time - travel scenarios. He might travel back in time to gain more knowledge or to prevent certain tragedies. Another one could be All Might. His past is full of secrets and his influence on the hero world is huge. Time travel could be used to explore more of his backstory or to change some crucial events in his past.