“AngularJS Onchange DateTime Picker no funciona” Código de respuesta

AngularJS Onchange DateTime Picker no funciona

<input mdc-datetime-picker date="false" time="true" type="text" id="time" short-time="true"
           placeholder="Time"
           min-date="minDate"
           format="hh:mm a"
           ng-model="time">


$scope.$watch('time', function() {
    alert('hey, time has changed!');
});