title: Issue: Fullcalendar shows 24 as midnight instead of 00:00
body: <p>For some reason, Fullcalendar is showing events that start past midnight as e.g. '24:15'. We want it to show '00:15'. I think this is a new issue, because we have had the calendar for a year, and this is the first I'm  hearing of it. But I can't find anything about how to solve it.
  <a href="https://i.stack.imgur.com/1yBLC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1yBLC.png" alt="Event in the calendar starting at 24:15"></a></p>
  
  <p>We are using fullcalendar v4.2.0. I did not write the original code, but I'm fairly familiar with it. We fetch events using a REST API, and we're using ServiceNow. When using the 12-hour format (am/pm), it shows 12a15. I tried changing the eventTimeFormat, but had no luck. This is part of the client script:</p>
  
  <pre><code>    /* Calendar */
  c.funcs.loadCalendar = function() {
      var calendarEl = document.getElementById('calendar');
      c.calendar = new FullCalendar.Calendar(calendarEl, {
          contentHeight: 'auto',
          plugins: [ 'dayGrid','timeGrid', 'list'],
          header: {
              left: 'prev next today',
              center: 'title',
              right: 'dayGridMonth,timeGridWeek,timeGridDay,listWeek,listMonth'
          },
          buttonText: {
              dayGridMonth: 'Month',
              timeGridWeek: 'Week',
              timeGridDay: 'Day',
              listWeek: 'List Week',
              listMonth: 'List Month',
              today: 'Today'
          },
          editable: false,
          eventTimeFormat: {
              hour: '2-digit',
              minute: '2-digit',
              hour12: false
          },
          eventOverlap: false,
          firstDay: 1,
          weekNumbers: true,
          // Scripted REST API which sends Start and End date-time of current view as parameters and gets current events. 
          //events: '/api/tnas/fullcalendar_fetch_data',
  
          events: function(info, successCallback, failureCallback) {
              $http({
                  method: 'GET',
                  url: '/api/tnas/fullcalendar_fetch_data',
                  headers: {
                      'X-UserToken': window.g_ck // Authorization
                  },
                  params: {
                      systems: c.vars.selectedSystems.map(function(system) { return system.value; }).toString(),
                      excludedTypes: c.vars.types.filter(function(type) {return !type.checked}).map(function(type) { if(!type.checked) return type.type   }).toString(),
                      start: info.start,
                      end: info.end
                  }
              }).success(function(data, status) {
                  successCallback(data.result.events);
              }).error(function(data, status) {failureCallback(data)});
          },
          loading: function(isLoading) {
              c.vars.calendarIsLoading = isLoading;
              $scope.$evalAsync();
          },
          // When event is rendered and put into the DOM, add a tippy.js tooltip to that element.
          eventRender: function(info) {
              tippy(info.el, {
                  theme: 'light-border',
                  content: info.event.extendedProps.tooltipContent,
                  arrow: true,
                  animation: 'fade',
                  flip: false,
                  boundary: 'window'
              });
          },
          eventClick: function(info){
              info.jsEvent.preventDefault();
              var p = $scope.data.page_id || 'form';
              var url = '/sp?id=' + p + '&amp;table=' + info.event.extendedProps.table + '&amp;sys_id=' + info.event.id + '&amp;view=sp';
              window.open(url, "_blank");
          },
          navLinks: true,
          navLinkDayClick: function(date, jsEvent) {
              //c.calendar.gotoDate(date);
              c.calendar.changeView('timeGridDay', date);
          }
      });
  
      c.calendar.render();
  }
  /* Calendar End */
  </code></pre>
  
  <p>JSON of the event:</p>
  
  <pre><code>title: "Metro IN-Applikasjoner - test"
  number: "SREL0004789"
  start: "2020-04-15 00:15:00"
  end: "2020-04-16 14:00:00"
  downtime_start: ""
  downtime_end: ""
  className: "SystemRelease"
  type: "system_release"
  table: "release"
  id: "4a393c2b298c54903eaa786081948e7c"
  state: "New"
  state_reason: null
  downtime_type: "Soft"
  color: "rgb(163, 222, 255, 0.5)"
  tooltipContent: "&lt;div style='text-align:left; font-size:1.5em'&gt;&lt;p&gt;Metro IN-Applikasjoner - test&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Start:&lt;/strong&gt;   00:15, 15. apr 20&lt;/p&gt;&lt;p&gt;&lt;strong&gt;End:&lt;/strong&gt;   14:00, 16. apr 20&lt;/p&gt;&lt;/div&gt;"
  </code></pre>
  
  <p>Hopefully someone has experienced the same issue before. Any help is greatly appreciated!</p>