Not sure if it's server sided or not, but I'm still able to change it to the lowest 1.1 sec and cast it in that time. Anything lower than that will not work. I've also tried 1 sec, but miss a lot. But the problem I'm having is, I've only found the pointer address, not the real one, so it changes everytime I start the game. If anyone can help me find the real one that would be great. I've only managed to get to the 3rd-4th level pointer and got stuck.
EDIT: I've found a way to get instant cast now, modify the "check time" to 0 and then you can change the cast time 0 and it will work. The problem still remains I don't know how to find the real address for either of the addresses, so I won't post the addresses cause it's useless and won't work for anyone else. I have to manually look for those address each and everytime I load the game. So does this mean it's not server sided like everyone thinks it is?