Here's an example of a Scheduled Apex class which will creates a new Case assigned to the Accountancy Queue. Once you have created and saved this class in your Production org, you can schedule it to run at the beginning of every month by going to: Setup > App Setup > Develop > Apex Classes > Schedule Apex. Select "CaseCreator" as the Apex Class to run, and then schedule it to run at the desired date/time intervals.

// 
// CaseCreator.cls --- can be scheduled to run at any time interval
//

global class CaseCreator implements Schedulable {

    // Callable from a Unit Test
    public void execute() {
        // Find the Accountancy Queue,
        // so that we can assign a new Case to it
        Group accountancyQueue;
       try {
            accountancyQueue = 
                [select Id 
                from Group 
                where Type = 'Queue' 
                and Name = 'Accountancy Queue' 
                limit 1];
        } catch (Exception ex) {
            System.debug('***Could not find Accountancy Queue');
        }
        if (accountancyQueue != null) {
            // Create a new Case assigned to the Accountancy Queue
            Case c = new Case(
                OwnerId = accountancyQueue.Id,
                Priority = 'Medium',
                Status = 'New',
                Subject = 'New Accountancy Queue Case',
                Description = 'Case Description'
            );
            // Try to insert our Case
            try {
                insert c;
            } catch (DMLException ex) {
                // Handle the error
            }
        }
    }

    global void execute(SchedulableContext sc) {
        execute();
    }

    /////////////////////
    // UNIT TESTS
    /////////////////////
    
    private static testMethod void TestCaseCreation() {
        // Try to obtain a reference to our Accountancy Queue
        Group accountancyQueue;
        Exception exCaught;
       try {
            accountancyQueue = 
                [select Id 
                from Group 
                where Type = 'Queue' 
                and Name = 'Accountancy Queue' 
                limit 1];
        } catch (Exception ex) {
            exCaught = ex;
        }
        System.assertEquals(null,exCaught,
            'Accountancy Queue not found. Please create it, then rerun this test.');
        
        // Now, simulate executing our Scheduled Case Creator.
        CaseCreator cc = new CaseCreator();
        cc.execute();
        
        // Verify that a new Case was created in the Accountancy Queue
        List<Case> cases
            = [select id, Subject
                from Case
                where OwnerId = :accountancyQueue.Id
                and CreatedDate = TODAY
                order by CreatedDate DESC
                limit 1];
        System.assertEquals(1,cases.size(),'cases.size()');
        
    }


}