Messaging window
The messaging window is Meta's rule that a business account may send standard messages only within 24 hours of the person's last message to it. Outside that window, ordinary automated follow-ups can't be sent until the person engages again.
Why it matters for creators
The window is why good automation answers instantly: the moment of engagement opens 24 hours of permitted conversation, and the first minutes are when a reply converts best anyway.
It also shapes strategy. You can't drip-message someone next Tuesday because they commented once today — the follow-up has to earn a fresh reply (or move the relationship to a channel you own, like email, via email capture). Tools that promise unlimited follow-up sequences on Instagram are describing something the platform doesn't permit.