When a GenerateCredentialReport call is invoked, IAM checks if there is an existing report. If the report was generated within the past four hours, the API call will use the most recent report rather than generating a new report. If the most recent report is older than four hours or there are no previous reports, the GenerateCredentialReport API generates a new report. For more information, see Getting credential reports for your AWS account.
Change the MaximumExecutionFrequency parameter to more than 4 hours. MaximumExecutionFrequency indicates the maximum frequency with which AWS Config runs evaluations for an AWS Managed Periodic rule.