JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/themes/ui-lightness/jquery-ui.css">
<input type="text" id="txt1" value="13/06/2013" />
<br />
<select id="ddlHourTime">
    <option>06</option>
    <option>08</option>
    <option>09</option>
    <option>10</option>
    <option>11</option>
    <option>12</option>
    <option>13</option>
    <option>14</option>
    <option>15</option>
    <option>16</option>
    <option>17</option>
    <option>18</option>
    <option>19</option>
</select>
<br />
<select id="ddlMinuteTime">
    <option>00</option>
    <option>15</option>
    <option>30</option>
    <option>45</option>
</select>
<br />
<br />
<input type="button" id="btn1" value="test" />

JavaScript

$(document).ready(function () {
    'use strict';
    var calcWorkHours = function calcWorkHours(start, end) {
            var total = (end - start) / (1000 * 60 * 60 * 24),  // compute difference in days
                totalDays = parseInt(total, 10),                // trim fractional portion
                remainder = (total - totalDays) * 24,           // save fractional portion in hours
                startingDay = start.getDay(),                   // starting weekday
                endingDay = end.getDay(),                       // ending weekday
                possibleWorkingDays = (totalDays * 5),
                actualOccuringWeekends = (startingDay - endingDay) * 2,
                workDays = (possibleWorkingDays - actualOccuringWeekends) / 7;
            if (endingDay === 6) {
                workDays -= 1;  // ends on a weekend, subtract a day
            }
            if (startingDay === 0) {
                workDays -= 1;  // starts on a weekend, subtract a day
            }
            return (workDays * 24) + remainder; // convert to hours and add back fractional portion
        },
        parseInputs = function parseInputs(date, hour, minute) {
            var dmy = date.split("/"),
                now = new Date(),
                thisMinute = now.getMonth() + 1 + "-" + now.getDate() + "-" + now.getFullYear() + " " + now.getHours() + ":" + now.getMinutes() + ":00",
                start = Date.parse(dmy[1] + "-" + dmy[0] + "-" + dmy[2] + " " + hour + ":" + minute + ":00"),
                end = Date.parse(thisMinute);
            start = new Date(start);
            end = new Date(end);
            return calcWorkHours(start, end);
        };
    $("#btn1").click(function (event) {
        var date = $("#txt1").val(),
            hour = $("#ddlHourTime").val(),
            minute = $("#ddlMinuteTime").val(),
            elapsed = parseInputs(date, hour, minute);
        window.alert(elapsed);
    });
    $('#txt1').datepicker({
       ...