How to pass datepicker value in form POST methed to PHP ?

Question

here's my HTML form

<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.4/jquery.min.js"></script>
<script type="text/javascript">
$(function () {
$('#datetimepicker1').datetimepicker();
});
</script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<!-- <link rel="stylesheet" type="text/css" href="css/bootstrap-datetimepicker.css"> -->
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.15.1/moment.min.js"></script>
<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.43/css/bootstrap-datetimepicker.min.css">
<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.43/css/bootstrap-datetimepicker-standalone.css">
<script type="text/javascript" src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-datetimepicker/4.17.43/js/bootstrap-datetimepicker.min.js"></script>
<script>
$(document).ready(function(){
$('[data-toggle="tooltip"]').tooltip();
});
</script>
<form action="one.php" method="POST">
<div class="col-md-6">
<div class="form-group">
<label for="name">Event Title:</label>
<input type="text" class="form-control" id="first_name" placeholder="Should be 10 character" required="" name="title" maxlength="10" >
</div>
<div class="form-group">
<label for="name">Client Name:</label>
<input type="text" class="form-control" id="first_name" placeholder="Enter Name" name="name" >
</div>
<div class="form-group">
<label for="text">Task:</label>
<input type="text" class="form-control" name="task" placeholder="Enter Task">
</div>
</div>
<div class="col-md-6">
<div class="form-group">
<label for="text">Set Date & Time:</label>
<div class="form-group">
<div class='input-group date' id='datetimepicker1' name="datepicker" value="date">
<input type='text' class="form-control" id="datepicker1" name="datepicker" value="date"/>
<span class="input-group-addon">
<span class="glyphicon glyphicon-calendar"></span>
</span>
</div>
</div>
</div>
<div class="form-group">
<label for="text">Department:</label>
<input type="text" class="form-control" name="department" placeholder="Select department " >
</div>
<div class="form-group">
<label for="text">Assign to:</label>
<input type="text" class="form-control" name="assign" placeholder="Select" >
</div>
<br><br>
<button type="submit" name="submitform" class="btn btn-default" style="float:right;width:auto; padding:10px; font-size:16px; background-color:rgba(0,0,0,0.8); color:white;">Submit</button>
</form>

AND Here's PHP

<?php
$servername = "localhost";
$username = "root";
$password = "";
$db = "admin";
// Create connection
$conn = new mysqli($servername,$username,$password,$db);
if(isset($_POST['submitform'])){
$title = $_POST['title'];
$name = $_POST['name'];
$department = $_POST['department'];
$task = $_POST['task'];
$date =$_POST['datepicker'];
$assign = $_POST['assign'];
$now =date('m/d/Y h:i:s a', time());
$query = "CREATE EVENT IF NOT EXISTS $title
ON SCHEDULE AT '$date'
DO
INSERT INTO task(name,department,task,assign,deadline,created_at) VALUES ('$name','$department','$task','$assign','$date','$now')
;";
mysqli_query($conn,$query);
echo "<center><br>Event has been created.<br/> You're notified that this will be fired automatically on your set date !<br/><br/>Redirecting back in 5 seconds ...";
header("Refresh: 1; url=test2.php");
mysqli_close($conn);
};
?>

Please guide, Please