The offer filter is news to me, too. And I have a shop on reverb! Both offers and counter offers do indeed expire if not responded to in 24 hours. When I get a ridiculous lowball offer, (which really doesn't happen all that often), I ignore it.
My pet peeve are messages where, rather than making an offer, they ask: "what's your best price?" I respond that my daddy taught me never to bid against myself. My price is the listing price. A potential buyer is always welcome to offer something less (I accept offers). I tell them that the more reasonable the offer, the more reasonable the response. It really is a game. I believe setting a higher price and entertaining offers gets me more action than just listing a set price, though the results will usually be the same final price.
Bill, tgo