Someone messages your Instagram on Friday afternoon asking whether you ship to their country. You see it Monday. You reply.
It doesn't send.
Not a bug: a rule. Business messaging on Meta's platforms operates inside a standard messaging window that opens when a person messages you and closes twenty-four hours later. Miss it and the conversation is over, from your side, permanently. Meta documents the policy in its Messenger Platform documentation.
Why the window exists
It's easy to read this as an obstacle. It's better understood as the thing that makes DM inboxes usable at all.
Without it, any business that ever received a message from you could message you forever. The window inverts the permission: the user grants access by messaging you, and the grant expires. You can respond to a conversation someone started; you can't start one whenever you like.
That's why it's a fixed clock rather than a preference: a preference would get ignored by exactly the businesses the rule exists to constrain.
What the clock actually does
It starts on their message, not yours. Every inbound message from that person resets it. A conversation that goes back and forth stays open indefinitely, as long as they keep participating.
It closes on silence. If they stop and you haven't replied within the day, the thread is closed to you.
It's per conversation. One expiring thread says nothing about the others.
The practical consequence: the awkward window isn't the busy conversation. It's the single question asked on a Friday night that nobody sees until Monday.
Running an inbox against a clock
Four things that make this manageable rather than stressful.
Check daily, not hourly. A once-a-day pass at a consistent time catches almost everything, because almost everything arrives with more than a few hours left. Hourly checking buys very little and costs your attention all day.
Sort by time remaining, not by arrival. This is the single change that matters most. An inbox ordered newest-first buries the message that's about to expire under three that arrived this morning and have twenty hours left. Urgency here is a function of the deadline, not of recency.
Have a floor for "acknowledge now, answer properly later". If a question needs research you can't do today, send a holding reply inside the window. That's not a fob-off: a reply resets nothing but it does keep you inside a conversation you can continue, because their next message will reopen the clock.
Decide what doesn't get a reply. Not every DM needs one. Spam, one-word reactions to a story, and messages that are really comments don't. Same triage logic as comments: most need nothing, a few need you specifically.
When you miss it
It happens. The thread is closed and you can't reply. Two honest options:
Answer it publicly instead, if the question is generally useful and you can do it without exposing who asked. A story or a post answering "do you ship to X" serves the person who asked and everyone else who wondered.
Wait for them to come back. Their next message reopens the window. Some will; most won't. That's the cost of the miss, and it's worth counting rather than shrugging at: a pattern of misses is an operational problem, not bad luck.
The other platforms
TikTok has no comment or messaging API available at the tier most businesses can access, so there's no equivalent workflow to build.
YouTube comments have no expiry at all: a comment from last year can still be replied to. Different mechanic entirely, and worth not confusing with DMs.
The window is a messaging rule specifically. It doesn't apply to public comments anywhere.
Where Acumin fits
The Engagement inbox computes the deadline from the last inbound message on each Instagram thread, and surfaces it as time remaining rather than as a timestamp, because "4h left" prompts an action and "yesterday 14:32" doesn't.
Threads escalate through tiers as the clock runs: calm, then warn at six hours remaining, then urgent under two. The soonest-expiring unanswered thread drives the alert on your Overview, the nav badge and the weekly digest line, so an expiring conversation reaches you even if you never open the inbox.
Two things worth knowing about how it handles your data:
Message bodies are never stored. Acumin persists thread metadata and a short snippet: enough to compute the deadline and show you what the thread is about. Full message bodies are fetched live when you open a thread and are not kept.
You send every reply. Acumin drafts in your brand voice; nothing is sent automatically. That's a deliberate constraint, and it's the reason the inbox is a workflow rather than an autoresponder.
How to use this tomorrow
Open your Instagram inbox and find the oldest unanswered message from someone who messaged you first.
Work out how long is left on it. If the answer is "it's gone", that's your baseline. And a daily fifteen-minute pass sorted by time remaining is almost certainly enough to make it the last one.
Related: Comment triage is the same discipline applied to public comments. Replying in brand voice covers what to actually write once you're inside the window.