You don't have to listen periodically. You just register once in the initialize. If anything changes in the model, this.asyncRender will be called.
Change here means any attributes set or removed or modified.
Try calling
this.model.set("title", "A Scandal in Bohemia");
and see this.asyncRender be called.
EDIT: If you want to manually poll for every 5 minutes, then you can check this.model.changed property. This is not advisable though.
http://backbonejs.org/#Model-changed
initialize: function() {
var self = this;
window.setInterval(function() {
if (self.model.changed) {
// Do your stuff
// this.asyncRender();
}
}, 5000);
}