Your observation matches what most owners see: the prospect who gets returned the fastest books. The difference between a polite "we'll call you back" and actually winning is treating an outbound callback like an inbound lead, with a target time and a short script.
Aim to return every unknown number inside two hours during the day, and by 10 the next morning for anything that comes in after hours. Speed matters more than perfection; the homeowner is still comparing options when you call back under two hours, and the window closes fast. When a call slips past four hours, switch to a text first so the prospect sees a real name instead of an unknown number.
Keep the return-call opening to three lines: confirm you're the contractor they reached out to, state what you want to do next in plain words, and lock a specific time rather than asking when they're free. "Thanks for reaching out about the kitchen. I'm putting together your estimate and I'll walk you through it Tuesday at 2 pm — does that work, or is 4 pm better?" Giving two tight choices is what turns a return call into a scheduled job.