Sony will carry out their PSN maintenance on the PlayStation 4 on Tuesday May 24th starting at 9:30pm PST and will last for around two hours.
Unless you’re already signed in, you will not be able to use any online services while the maintenance is going on if you’re on a PlayStation 4. Note that all other platforms are not affected. However, if you are signed in before the maintenance starts, then you will be able to access “most” of the applications and features without too much trouble.
“We strive to ensure that PlayStation Network services are available at all times, but occasionally we must take PlayStation Network offline to perform essential maintenance and implement feature enhancements. We are working hard to reduce the duration of each maintenance”
“We apologize for any inconvenience.”
You can find out more information here on the PSN Service Status page.