About the experiment, how can Libet conclusively derive the decision came after the initial EEG measurement. I mean how did he know the duration it takes to report the decision. The origin of the decision to being able to reflect on it may take a variable amount of time therefore invalidating the claim.

Also the strict separation of conscious/unconsciousness seems simplistic. Most actions may very well be processed subconsciously with very little decision making bubbling up to consciousness. Driving a car comes to mind. This also means when asking a subject to process something impulsively the vast majority of their actions may be subconscious.

tl;dr People spacing out does not invalidate free will.