SiteScripts/DefaultRegionalSettings.json

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/site-design-script-actions.schema.json",
  "actions": [
    {
      "verb": "setRegionalSettings",
      "timeZone": 10,
      "locale": 1033,
      "sortOrder": 25,
      "hourFormat": "12"
    }
  ]
}