Advice about optimal posting times comes from an era when feeds were chronological. Ranking replaced chronology, and the mechanism that made timing important no longer operates the way it did.
Chronological feeds made timing decisive
When posts appeared in the order they were published, a post's visibility depended entirely on who happened to be looking at that moment. Publishing into a quiet hour meant being buried by the time the audience arrived.
Under those conditions, posting when the audience was active was straightforwardly correct, and the advice was sound rather than superstitious.
It also made the competitive set very small, since a post only competed with whatever else was published in the same few minutes.
Ranking changed what a post competes against
Ranked feeds select from everything available and unseen, scored by predicted interest for that specific viewer. Publication time becomes one input among many rather than the organising principle.
A post published overnight can surface at midday if the system predicts it will perform, and a post published at the ideal hour can fail to surface at all.
The competitive set expands accordingly. A post competes with days of accumulated content and with material from accounts the viewer does not follow.
Early response still carries information
Timing has not become irrelevant, because ranking systems use early engagement as evidence of quality. A post that performs well in its first exposures is shown more widely.
Publishing when the audience is active therefore improves the quality of that early sample, which can influence how far the post travels afterwards.
The effect is real and much smaller than the original mechanism was, and it is dominated by whether the content itself holds attention.
The advice persisted because it is easy to follow
A posting schedule is concrete, requires no judgment about content, and can be implemented by anyone with a calendar.
Recommendations about what makes a post worth ranking are harder to act on and harder to sell, so the timing advice outlived the conditions that produced it.
Published charts of optimal hours also circulate long after the platforms they described have changed their ranking behaviour entirely.
What is worth testing instead
Your own account data is the only reliable source, since audience activity varies by market, category and follower composition rather than following a general rule.
The larger variable in almost every account is format, because platforms actively promote whichever format they are trying to grow and demote the rest.
Tracking which formats the system is currently favouring changes reach far more than moving a publishing slot by two hours ever will.