What is the longest voicemail greeting that still gets callbacks in your business?

YouTube and industry blogs will tell you to keep the voicemail under 20 seconds, but I've noticed real callers behave differently when they leave a message for a service business. How long is the voicemail greeting in your own company before callers just hang up and try the next number? Do people who hear the hours, a name, and the callback number actually call back, or do most callbacks come only when the greeting is a short 'we're out in the field, leave a message'? What greeting length are you running and what kind of callback rate does it produce in your experience?