Send an email after 4 hours of Inactivity on Cases

I have a requirement wherein we need to send an email to a group of users if cases is not assigned within 4 hours after it gets created.

• The case is getting created in salesforce using Email-To-Case and assigned to Queue as default case owner.

I've written a SOQL query which gives case records that are updated in last 4 hours but not sure how we can get cases which are not updated or not have actioned in 4 hours after cases's created time.

List<Case> casesUpdatedInLastFourHours = [select id, Subject, LastModifiedDate from Case where LastModifiedDate = TODAY AND HOUR_IN_DAY(LastModifiedDate) > 4];