JSFiddle - React, Tailwind, and code Playground

HTML

<label for="rabotaZapochva" style="display:inline;">РАБОТА ЗАПОЧВА:</label>
<select name="rabotaZapochva" id="rabotaZapochva" style="display: inline;width: 90px;font-size: 19px;font-weight: bold;">                       
  <option>Час:</option>
  <option>00:15</option>
  <option>00:30</option>
  <option>00:45</option>
  <option>01:00</option>
  <option>01:15</option>
  <option>01:30</option>
  <option>01:45</option>
  <option>02:00</option>
  <option>02:15</option>
  <option>02:30</option>
  <option>02:45</option>
  <option>03:00</option>
  <option>03:15</option>
  <option>03:30</option>
  <option>03:45</option>
  <option>04:00</option>
  <option>04:15</option>
  <option>04:30</option>
  <option>04:45</option>
  <option>05:00</option>
  <option>05:15</option>
  <option>05:30</option>
  <option>05:45</option>
  <option>06:00</option>
  <option>06:15</option>
  <option>06:30</option>
  <option>06:45</option>
  <option>07:00</option>
  <option>07:15</option>
  <option>07:30</option>
  <option>07:45</option>
  <option>08:00</option>
  <option>08:15</option>
  <option>08:30</option>
  <option>08:45</option>
  <option>09:00</option>
  <option>09:15</option>
  <option>09:30</option>
  <option>09:45</option>
  <option>10:00</option>
  <option>10:15</option>
  <option>10:30</option>
  <option>10:45</option>
  <option>11:00</option>
  <option>11:15</option>
  <option>11:30</option>
  <option>11:45</option>
  <option>12:00</option>
  <option>12:15</option>
  <option>12:30</option>
  <option>12:45</option>
  <option>13:00</option>
  <option>13:15</option>
  <option>13:30</option>
  <option>13:45</option>
  <option>14:00</option>
  <option>14:15</option>
  <option>14:30</option>
  <option>14:45</option>
  <option>15:00</option>
  <option>15:15</option>
  <option>15:30</option>
  <option>15:45</option>
  <option>16:00</option>
  <option>16:15</option>
  <option>16:30</option>
  <option>16:45</option>
  <option>17:00</option>
  <option>17:15</option>
  <option>17:30</option>
 ...

JavaScript

$(document).ready(function() {
  $("#rabotaZapochva").change(workingAtNight);
  $("#rabotaShvyrshva").change(workingAtNight);
});

function workingAtNight () {
        var start_time = $('#rabotaZapochva').val();
        var end_time = $('#rabotaShvyrshva').val();
        if(end_time > "06:00" && end_time < "22:00"){
            end_time = "06:00";
        }


        if((end_time > "22:00") || (end_time < "06:00")){
            if(start_time > "22:00" || (start_time > "00:00" && start_time < "06:00")){
                start_time = $('#rabotaZapochva').val();
            }
            else{
                start_time = "22:00";
            }
        }
        else{
            start_time = $('#rabotaZapochva').val();
        }


        var diff = ( new Date("1970-1-1 " + end_time) - new Date("1970-1-1 " + start_time) ) / 60000 / 60;

        var sumaNoshtenTrud = 0;

        var decimalTimeString = diff;
        var n = new Date(0,0);
        n.setSeconds(+decimalTimeString * 60 * 60);
        var test = n.toTimeString().slice(0, 5);
        if(test > "08:00"){
            test = "08:00";
        }


        if(start_time >= "06:00" && start_time < "22:00"){
            test = "00:00";
        }



        $('#noshtenTrud').val(test);
        
        

    };