First off, Kira would be able to beat Diavolo, while Diavolo can skip time to see that Kira is indeed the stand user of Killer Queen, that probably might causes Bites the Dust to activate since Diavolo would then know Kira's identity. Since Diavolo is blown to bits in this scenario it is canon.
Second, DIO's timestop won't do anything to Kars, no matter how many knives, punches or road rollers DIO throws at Kars won't do anything since Kars is unkillable. What's more if Kars is capable of mimicking the abilities of every other lifeform on the planet, including hamon, then Kars being able to use his own version of the World isn't much of a stretch. Jorge Joestar isn't really canon, but it does give us a good idea on how powerful Kars actually is.