How to check multiple selectors to trigger an event?

New to jquery but I am working on a responsive calendar. Now I have a start date and an end date field. If the end date is populated, the reoccurrence check box shows as it removes it from the not-visible class.

How can I add a check on the start date also? I want the check box to show when both of the start and end fields are filled not just one.

 $("#end_date").on("input", function (){
            if($('#end_date').length >= 1) {
                $("#reoccurrence").removeClass('not-visible');
            } else {
                $("#reoccurrence").addClass('not-visible');
            }
        });
.not-visible {
    display: none;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="col">
  <div class="md-form md-form-container-fix">
    <input type="text" id="start_date" class="form-control date-picker" name="start_date" required />
    <label for="start_date">Start Date</label>
  </div>
</div>

<div class="col">
  <div class="md-form md-form-container-fix">
    <input type="text" id="end_date" class="form-control date-picker" name="end_date" required />
    <label for="end_date">End Date</label>
  </div> 
</div>

<div class="form-check not-visible" id="reoccurrence" name="reoccurrence">
  <input class="form-check-input" type="checkbox" id="is_reoccurring" name="is_reoccurring" value="1" />
  <label class="form-check-label" for="is_reoccurring"> Reoccurrence? </label>
</div>