Simple Time-Dependent Workflow Action in Salesforce

Below configuration with Workflow will send SLA Notification to the Account owner 30 day before the SLA Expiration Date. 

Email Template:

Email Alert:

Workflow Rule:

 To test

1. Open an Account Record.

2. Edit it and set Active to Yes and SLA Expiration Date to a future date.

3. Go to in Setup and click Search button.