The Premier Add On allows you to set a scheduled interval using the built-in WordPress Cron scheduler to calculate the initial distance for locations where the distance is zero.
The initial distance setting is used by Store Locator Plus to boost performance when loading the initial map. It uses and SQL index on a numeric value to select a subset of data versus calculating values for potentially thousands of locations and then filtering based on the calculation. For sites with more than 1,000 locations this feature significantly boosts initial map loading performance.