My Mind Freeze is its own mapped key.
It has four steps, because I have four DK's.

On each step, it sends my warcraft keybind for Mind Freeze to one DK only.
I check the box, "Do Not Advance For" and set it to 2.5 seconds.
Which means no matter how often I spam this mapped key (or another mapped key calls it), it sticks on each step for 2.5 seconds before advancing to the next step.



I then include (in my main DPS/Spammed mapped key) an action for:
- Do Mapped Key, the Mind Freeze mapped key.

So when I spam my main DPS key, it attempts to do the Mind Freeze on every press.
However, after the first press (Step 1) it cannot advance to Step 2 (DK #2) for 2.5 seconds.
Once at least 2.5 seconds have passed, the next push of my main key also attempts the Mind Freeze mapped key, via the Do Mapped Key action, and this time the Mind Freeze mapped key can fire off.
It is still in response to a key stroke and not automated in any way.

Because the Mind Freeze is runic power and rune free, plus off of the GCD, anytime it is called the spell is instant cast.