Apparently this is how FullCalendar works and the end is exclusive (rather than
inclusive) on the calendar, which means they are always one day too short on the
calendar.

https://stackoverflow.com/questions/27604359/fullcalendar-event-spanning-all-day-are-one-day-too-short

A fix for this is to add the following to the FullCalendar Jquery Call ...

eventDataTransform: function(event) {
 if(event.allDay) {
  event.end = moment(event.end).add(1, 'days')
 }
 return event;
},


Any chance, this can be added to the templates within your module?