php语法如何对过期实现自动结算

<?php
/* 连接到数据库 */
$mysqli = new mysqli('localhost', 'username', 'password', 'database_name');
if ($mysqli->connect_errno) {
  echo "Failed to connect to MySQL: " . $mysqli->connect_error;
  exit();
}
 
/* 设置时区 */
date_default_timezone_set('Asia/Shanghai');
 
/* 订单有效期 */
$valid_period = 3600; /* 一小时 */
 
/* 遍历订单列表 */
$sql = "SELECT * FROM order_table WHERE status = 'pending'";
$order_result = $mysqli->query($sql);
while ($order_row = $order_result->fetch_assoc()) {
  /* 订单超时 */
  $order_time = strtotime($order_row['add_time']);
  if (time() - $order_time > $valid_period) {
    /* 取消订单 */
    $sql = "UPDATE order_table SET status = 'cancelled' WHERE order_id = ".$order_row['order_id'];
    if (!$mysqli->query($sql)) {
      echo "Error: " . $mysqli->error;
    }
  
    /* 结算金额 */
    $amount = $order_row['amount'];
  
    /* 更新卖家账户余额 */
    $sql = "UPDATE seller_table SET balance = balance + ".$amount." WHERE seller_id = ".$order_row['seller_id'];
    if (!$mysqli->query($sql)) {
      echo "Error: " . $mysqli->error;
    }
  
    /* 更新买家账户余额 */
    $sql = "UPDATE buyer_table SET balance = balance - ".$amount." WHERE buyer_id = ".$order_row['buyer_id'];
    if (!$mysqli->query($sql)) {
      echo "Error: " . $mysqli->error;
    }
  }
}

$mysqli->close();
?>