SELECT DATE_FORMAT(`time_on`,'%H:%i'),`icon_path`,`name_of_scene`,`detal_descr`,`type`,`date_on`,`day_of_week`,`timeout`,`exec_scene` FROM `scenes` WHERE `name_of_scene` = 'привет медвед' 

Notice:  Undefined index: time_on in /var/www/html/

while ( $scenes_array = mysqli_fetch_assoc($scenes_qr) )  							
	{
             echo '<b>Время запуска:</b> '.$scenes_array['time_on'];
        }

DATE_FORMAT(`time_on`,'%H:%i')AS `time_on`

if(empty($_GET['start_time'])) {$start_time_qr="IF(`time_on` IS NULL,NULL,NULL)AS `time_on`";}
				else {$start_time_qr="IF(`time_on` IS NULL,'$start_time','$start_time')AS `time_on`";}
$query="INSERT INTO `scenes`(`time_on`)SELECT 
".$start_time_qr."
FROM `scenes` WHERE `name_of_scene` = '$scene_name'";

if($start_time=='') {$start_time=NULL;}
$query="INSERT INTO `scenes`(`time_on`)SELECT 
IF(`time_on` IS NULL,$start_time,'$start_time')AS `time_on`
FROM `scenes` WHERE `name_of_scene` = '$scene_name'";