ShowingTime can be turned off on a per-agent basis by either the agent or someone with office level permissions.

Agent Opt Out Instructions: Click on "My Agent Setup" on the left side menu. Then, turn “Allow Agents to Request Appointments Online” to “No,” as seen below. 

Broker or Office Admin Opt Out Instructions: Navigate to “Our Agents and Staff” on the left side menu, and then choose the agent to switch off. You'll see the same setting options as an agent would see (like in the above photo).