Briefly Unavailable For Scheduled Maintenance is a notification that usually appears on our website, when the theme/plugin update process in wordpress is being done.
Sometimes the update process is not carried out perfectly.
Or there is an error that occurs in the middle of the ongoing process.
So we can’t access our website, and also our wordpress admin panel too.
For that, do the following steps to eliminate the Briefly Unavailable For Scheduled Maintenance display.

• Please go to your blog’s webhosting cPanel or xampp/htdocs/folderwordepressanda folder
• After successfully logging in, please open the file manager then public_html
• After going into the public_html folder, you ‘ll find a file called .maintenance.
  This is the file that’s causing WordPress to crash.
  To fix the error, delete the .maintenance file and reload your blog dashboard.
  If you can’t find the file, check “Show Hidden Files” first.
• Finish.

Try accessing your wordpress amen panel and your website again.
Good luck.