JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<input type="text" id="timeOfCall" >
<input type="text" id="timeOfResponse">

<input type="text" id="delay">

JavaScript

$(document).ready(function(){
  $("input").keyup(function(){
      var timeOfCall = $('#timeOfCall').val(),
          timeOfResponse = $('#timeOfResponse').val(),
       hours = timeOfResponse.split(':')[0] - timeOfCall.split(':')[0],
          minutes = timeOfResponse.split(':')[1] - timeOfCall.split(':')[1];

      if (timeOfCall <= "12:00:00" && timeOfResponse >= "13:00:00"){
        a = 1;
      } else {
        a = 0;
      }
      minutes = minutes.toString().length<2?'0'+minutes:minutes;
      if(minutes<0){ 
          hours--;
          minutes = 60 + minutes;        
      }
      hours = hours.toString().length<2?'0'+hours:hours;

      $('#delay').val(hours-a+ ':' + minutes);
  });
});