Itachi activated Susano'o before an already travelling Kirin hit him. There's really no proof that he can't activate a V3 Susano'o in such a little amount of time since activating Susano'o is just using Chakra to make it. He just uses up a bit more Chakra, not to mention he'll see Chakra building up in Kakashi's eye.
Either way, Dusk Crow Genjutsu puts Itachi under a Genjutsu before he even realizes what's going on and then this ends with a speedblitz and Kakashi's head rolling under his feet before he even realizes that he is in a Genjutsu or thinks about breaking out of it.
1) Just a lil bit more chakra? The difference of power between v2 and v3 is big, Itachi would take more time to activate V3.
2) He will se the chakra building up on kakashi's eye? Kakashi's kamui works faster than Obito's sight, Itachi won't see it, or he will just see it but wont be able to react to it.
3) Itachi has no feat of putting v3 susanoo of an instant, so by MANGA FEATS, he can't put up yata faster than kakashi's kamui, maybe he could if we had seen more of his battles while he was alive, but sadly, that's not part of his feats, so forgive me for just following what manga says.
4) Crow genjutsu? Kakashi has knowledge of Itachi, he wouldn't fall for that, also dont forget Kakashi didn't get caught on Obito's genjutsu, a med level genjutsu wont work on him.