The Toki Toki no Mi is a Paramecia-type Devil Fruit that allows the user to send themselves and/or others forward in time. It was eaten by Kozuki Toki, but with her death, the fruit has returned into circulation.
So far, the only strength of the fruit is the user's ability to transport themselves and/or others into the future. This can be useful for getting out of dangerous situations. The user is also apparently able to decide the specific amount of time skipped for each trip.
The seeming maximum for traveling to the future each time is 20 years, though it's unknown if the user can travel even further than that.
It is impossible to travel into the past, meaning that any and all trips forward in time are irreversible. Also, the fruit's power cannot teleport the travelers to other locations, meaning that the user must be careful of where they or others are standing at the moment of the time-jump. Otherwise, the user is affected by the standard Devil Fruit weaknesses.
During her life, Toki had used this ability to travel further and further into the future, allowing her to live in many different time periods. Whenever she found herself cornered by some apparent threat, Toki could activate her ability in order to escape it, moving forward to a time period where the threat was not present anymore.
The final time she used this fruit was to enable her son Momonosuke and four of her retainers to escape from the burning of Oden Castle, sending them 20 years into the future.
At least 830 years ago, Toki ate the fruit and gained the ability to time travel to the future, having used the fruits ability to travel and live from one time period to the next, eventually landing herself 30 years before the present where she finally settled down and married Kozuki Oden.
She last used her ability to send her son and half of the Nine Red Scabbards twenty years in the future. Following her death, the Devil Fruit returned to circulation.