Need to show hours as 07:00, 15:00, 23:00 (8 hrs increment) in timefield

I need to show hours as 07:00, 15:00, 23:00 (8 hrs increment) in timefield, but when I used the following code, it is not giving the desired output, can some one help me, if I am missing something.

Code:

Ext.create('Ext.form.Panel', {
    title: 'Time Card',
    width: 300,
    bodyPadding: 10,
    renderTo: Ext.getBody(),
    items: [{
        xtype: 'timefield',
        name: 'in',
        fieldLabel: 'Time In',
        format : 'H:i',
        minValue: '07:00',
        maxValue: '23:00',
        increment: 480,
        anchor: '100%'
    }]
});

Thanks in Advance.



Need to show hours as 07:00, 15:00, 23:00 (8 hrs increment) in timefield