How to code against logic that depends on the current time in AngularJS?

I have some code and the result of it depends on the current time. Say,

Shop.prototype.isOpen = function() {
  var now = new Date();
  var today = now.getDay();

  return this.openTime(today) <= now && now <= this.closeTime(today);
};

And then in the view, we display whether a shop is open:

<span ng-show="shop.isOpen()">Open now!</span>

The isOpen method is called once and doesn't get updated after that.

I have lots of complex application logic that depends on the isOpen and similar "time-bound" data.

What are the general approaches to keep the isOpen data fresh and have application logic/view be constantly in sync with that?

I think one solution would be to have an intermediate object whose value gets updated in frequent intervals, but I'm not sure if this is the right approach.