Our voice mail has a message during the school year. It says something like, please call back after 3pm or leave a message.
When my two were younger, I had a message on the door bell that said visitors were welcome after 2pm, and I had a sticky note by the phone that read..."No, I'm sorry it's not possible."
People get used to consistency, but you have to get comfy saying no or later. You need to show that you value your time in order for others to get it. kwim?