Pressing the third key a fraction of a second later than the second one would, I guess, be hard to avoid but difficult to interpret for the computer.
Forgive my ignoranace, but how is it different than any other keystroke combination? IOW, why is the timing between, say, CMD+F+V any more critical than between CMD+OPT+F?
CMD, OPT, ALT, CTL, SHIFT are all modifier keys. They change the key code that's sent from the keyboard to the computer. I believe all that's handled at the keyboard level, not at the software level.
CMD, OPT, ALT, CTL, SHIFT are all modifier keys.
I operate under the same assumption.
So command-X being pressed a fraction of a second earlier than the additional key Y would, I suspect, be handed off to the OS as command-X.