No error but not working while retrieving data from mysql DB through PHP

<?php if(isset($_POST['submit'])) { $username = $_POST['in']; $Timein= date("Y-m-d H:i:s",strtotime(str_replace('/','-',$username))); $username = $_POST['out']; $Timeout = date("Y-m-d H:i:s",strtotime(str_replace('/','-',$username))); $dbc = mysqli_connect('localhost','dev','dev@123','HireCamera') or die('Error while connecting Database'.mysql_connect_error); $q="select * from camera where NOT chkin > '$Timein' AND NOT chkout < '$Timeout'"; $r = mysqli_query($dbc,$q); while ($data = mysqli_fetch_assoc($r)) {?>
								<div class="col-lg-3 col-md-3 col-sm-6 col-xs-6 col-xxs-12">
									<div class="tm-tours-box-2">						
										<img src="img/index-0 <?php echo $data['id'];?>.jpg" alt="image" class="img-responsive">
										<div class="tm-tours-box-2-info">
											<h3 class="margin-bottom-15"><?php echo $data['name']; ?></h3>
											<p>Rs <?php echo $data['price']; ?>/day</p>	
										<a  class="tm-tours-box-2-link" onclick="POP()">Book Now</a>


first you should name your variables according to what they store, makes it easier to understand, or remove them if they’re not needed more than once:

$username = $_POST['in'];
$Timein= date("Y-m-d H:i:s",strtotime(str_replace('/','-',$username)));

could be changed to

// strtotime is clever enough to handle both `/` and `-` in dates
$Timein= date("Y-m-d H:i:s", $_POST['in']); 

Next, logic in SQL operands is a tad confusing.
Instead of NOT < and NOT >
you can change it to

$q="select * from camera where chkin <= '$Timein' AND chkout >= '$Timeout'";						

Finally, do you actually have data in your DB that matches the above conditions?

ps: you should also make sure $_POST['in'] and $_POST['out'] are not empty