php - mysqli Query throws a notice : Trying to get property of non-objec

$startTime = "09:30";

 $sql_monday = "SET @VALUE = '".$startTime."';
    SELECT * FROM schedule_orders 
    WHERE  @VALUE >= DATE_FORMAT(start_time, '%H:%i') 
    AND  @VALUE <= DATE_FORMAT(end_time, '%H:%i');";


    $result = $conn->query($sql_monday);
    if ($result->num_rows > 0) {
        // output data of each row
        while($All_monday_Orders = $result->fetch_assoc()) {
            $All_monday_Orders['id'];
        }
    }

Above is my Code which throws me a Notice

Notice: Trying to get property of non-object in on line if
($result->num_rows > 0)

if i echo this query and run in phpMyadmin , it showing results.

am i doing anything wrong here in this query ?