The ending of Star Wars: The Clone Wars season 7 sees Darth Vader discover Ahsoka Tano's lightsabers on an unnamed snowy moon, but leaves things a little unclear as to how long after Revenge of the Sith this takes place in the Star Wars timeline. The Clone Wars held off fully introducing Vader until its very final scene, although the show as a whole built up to his transformation. Through Anakin Skywalker, Obi-Wan Kenobi, and Ahsoka, there was plenty of opportunity for the seeds to be planted for his turn to the dark side, with The Clone Wars able to better flesh that out.
That paid off in the last scene of The Clone Wars season 7 finale, "Victory & Death", which also served as the series finale of the animated Star Wars show. Ahsoka faked her death after crashing on the moon following the Siege of Mandalore, burying her lightsabers at a makeshift graveyard for the deceased clone troopers. Sometime later, Darth Vader himself visits the planet and, standing in front of the trooper helmet that marks the site, finds one of Ahsoka's lightsabers in the snow. Since this is very much Darth Vader, complete with the iconic black costume, it obviously has to take place after Revenge of the Sith, but exactly when is left unclear by the show.
The finale of The Clone Wars does offer a few hints as to when the scene takes place, including the presence of Snowtroopers, and Vader's red lightsaber, which can be seen hanging at his side. Snowtroopers were introduced after the Galactic Empire had started to cement its position and replaced the clone troopers with Stormtroopers (who can also be seen in The Clone Wars' final moments). They could still be clones in the armor, but that switch still took some time to happen. Darth Vader, meanwhile, forged his red lightsaber after hunting down and killing the Jedi Kirak Infil'a. That happened at some point in 19BBY, the same year Revenge of the Sith takes place, but likely at least a few months afterwards, as covered in the Darth Vader: Dark Lord of the Sith comics. Giving enough time for these things to all happen, that means the scene in The Clone Wars likely takes place roughly one year after the events of Revenge of the Sith at the least.
On top of that, this is presented as Vader discovering Ahsoka is still alive thanks to the presence of Morai, in turn suggesting it's before they come into contact with one another again in Star Wars Rebels, which begins in the year 5BBY, and season 2 (which is when their meeting happens) starting in 4BBY. That itself is slightly complicated by his words there, though - "the apprentice lives" - which indicates surprise at her survival. That might offer either a different interpretation of this finale scene - Vader really does believe Ahsoka is dead - or that it takes place after Rebels. However, Darth Vader finding Ahsoka's lightsabers likely takes place much earlier in the timeline than that, so it's either more likely that former, or something else causes his surprise.
It makes sense for The Clone Wars to keep things at least somewhat close to the series' established timeline. After all, this is about completing Anakin's arc, with this moment symbolizing him truly becoming Darth Vader and leaving what's left of Anakin behind. Given many of Vader's most ruthless acts have been charted in the time period between Revenge of the Sith and Rogue One and Star Wars: A New Hope, this has to be still relatively close to Revenge of the Sith, within a few years at most, rather than a decade or more later when those lingering shreds of humanity are long gone. What's more, the final shot, seen through the trooper helmet, is very much signifying the end of the clone wars era too. It doesn't work to have that so late in the timeline. It fits best that this is around 18BBY, one year after Revenge of the Sith, or at most another 2-3 years later, giving a true ending to The Clone Wars that keeps it within that period.