<select class="form-control custom-select" ng-model="value">
    <option value="0" selected="selected">once per day</option>
    <option value="180">every 3 hours</option>
    <option value="120">every 2 hours</option>
    <option value="60">every hour</option>
    <option value="30">every 30 minutes</option>
    <option value="15">every 15 minutes</option>
    <option value="10">every 10 minutes</option>
    <option value="5">every 5 minutes</option>
</select>
