The response window is the promise that actually matters in an emergency: how soon a qualified technician will be standing at your door. The language is slippery, so it pays to know what each term really means.
True 24/7 emergency service means a live dispatcher answers at any hour and a technician can be dispatched overnight, on weekends, and on holidays. That is very different from an answering service, which simply records your message after hours and promises a callback during the next business day — useful, but not help at 1 a.m. Same-day service is its own category: it means arrival within stated hours that calendar day, not necessarily round-the-clock availability. A shop can honestly offer same-day without being a true 24/7 operation.
Two follow-up questions cut through the marketing. First, ask for a stated arrival window — 'within two hours,' 'before 6 p.m.' — rather than a vague 'we'll get to you,' and get it in writing or by text. Second, ask whether the truck is stocked to fix the problem on the first visit: a fast arrival means little if the tech diagnoses the issue, then leaves to order a capacitor or contactor and returns tomorrow. In a heat emergency — especially in a home with an elderly or medically vulnerable resident — a realistic, committed window plus a stocked truck beats the biggest '24/7' banner.