One quick and easy way to increase the experience for your clients is to add a custom maintenance page design to WordPress. This page will automatically display when WordPress or WordPress plugins are upgrading. It will replace the out of the box solution that displays a basic Times Roman “Briefly Unavailable for Scheduled Maintenance” message.
Customize Your Maintenance Page
Create a new file in your WordPress installation:
/wp-content/maintenance.php. This file will always be kept independent of core upgrades.
Sorry! We're doing some routine maintenance.
We're on a quick coffee break.
Our site is undergoing a brief bit of maintenance that will last 5 minutes at the very most.
We apologize for the inconvenience, we're doing out best to get things back to working order for you.
Keep in mind that you won’t be able to use WordPress functions in this file, think of it as a standalone HTML file that is external from WordPress.