First let's acknowledge that "Has it ever existed before?" is not helping with conclusion outside "it proved not physically impossible for some time in some historical specific context". It would not tell anything about "is that possible now or in near future in this or that specific geopolitical context at such a scale". And if it never existed before, a first in history is always possible.
Now what get often cited as direct democracy is ancient Greek city-states and nowadays Switzerland, which are two vastly different implementations.
> How would citizens even have the time?
That's actually the exact opposite mindset of what it takes to think democratically: how one could be called a citizen when they are not equipped with everything it takes to properly accomplish citizen duties. Of course accomplishing civil duties should be fairly compensated for the time invested. Such a compensation is generally existing and expected by current politician, so the only difference with direct democracy on this regard is that it should not be reserved to a small cast.