There's a server side check, the only thing you get when you remove the client-side cooldown is more spam in your logs...
The count down is actually pretty easy to find, its player pointer + 0x1944 (I think out of the top of my head), it'll contain the value '1500', if you set this to 0 you have no GCD on your client. (if its not 0x1944, look around that offset)