问Ember.JS绑定到时间？

EN

{{#each callback in App.callbackController}}
    <tr>
        <td align="center" {{bindAttr style="callback.urgent"}}>{{callback.formatted_time}}</td>
    </tr>
{{/each}}

App.Callback = Ember.Object.extend({
    date_time: null,
    urgent: function()
    {
        current_time  = new Date().getTime();
        callback_time = new Date(this.get('date_time')).getTime();

        if(((callback_time - current_time) / 1000 / 60 * -1) > 30)
        {
            return 'color: #FFF; font-weight: bold; background: #'+Helpers.colours.red;
        } else {
            return 'color: #FFF; font-weight: bold; background: #'+Helpers.colours.green;
        }
    }.property('date_time')
});