blah.html

                <form name="myForm">
                    <label for="duration"> Duration: </label><br>
                    <select name="duration" ng-model="selectedDuration" ng-change="durationChange()">
                        <option ng-repeat="(key, value) in durations" value="{{value}}" selected="{{isSelectedDurationOption(value)}}">
                            {{key}}
                        </option>
                    </select>
                </form>

blah.js

  $scope.durations = {
    "15 minutes": 900,
    "1 hour": 3600,
    "8 hours": 28800,
    "16 hours": 57600,
    "24 hours": 86400
  };
  $scope.selectedDuration = 3600;
  $scope.durationChange = function(){
    console.log("selection changed to " + $scope.selectedDuration);
  };
  $scope.isSelectedDurationOption = function(value){
    if(value == $scope.selectedDuration){
      return 'selected';
    }
    return 'false';
  };