如何在smtp消息体中添加函数，每12小时发送一次？

import smtplib
import time

from email.mime.text import MIMEText

def send_email():
    # 构造邮件内容
    msg = MIMEText('这是一封定时发送的邮件', 'plain', 'utf-8')
    msg['From'] = 'sender@example.com'
    msg['To'] = 'receiver@example.com'
    msg['Subject'] = '定时发送邮件示例'

    # 发送邮件
    smtp_server = 'smtp.example.com'
    smtp_port = 587
    smtp_username = 'username'
    smtp_password = 'password'
    smtp_sender = 'sender@example.com'
    smtp_receiver = 'receiver@example.com'
    
    try:
        smtp = smtplib.SMTP(smtp_server, smtp_port)
        smtp.starttls()
        smtp.login(smtp_username, smtp_password)
        smtp.sendmail(smtp_sender, smtp_receiver, msg.as_string())
        smtp.quit()
        print('邮件发送成功')
    except Exception as e:
        print('邮件发送失败:', e)

# 定时发送邮件
while True:
    send_email()
    time.sleep(12 * 60 * 60)  # 等待12小时后再次发送