There's no single best way to craft an after hours greeting. The most important point is that you equip your customers with what they need to know, and give them an avenue to contact you, whether that's through voicemail, email, or other channels.
“Hello ____. This is _____ again, calling from ______. I ran across some information on a client who made dozens of offers on houses before someone finally accepted one of them. We learned a lot from the experienced and I successfully used the findings to help other homebuyers make bids that were accepted early in the house hunting process. I thought I would share it with you in hopes of saving you time and making it easier for you to purchase the home of your dreams. I’ll email you the information. Give me a call if you would like to review it together. Thank you.”

I personally hate leaving voicemail messages because more times than not, I never hear back from the person I left a message with.
Hello, you have reached Dr. X. Right now, I am with a patient, so I’m unable to respond to your call immediately. If you need help with a prescription, call number Y. If you need to book/modify an appointment, call number z. Please, leave your name, and phone number and reasons for calling.