Sony announced today that PlayStation Network is scheduled for maintenance on Monday, March 23. The service will be down for two hours and a half starting with 16:00, until 18:30 GMT. As you probably know, you won’t be able to login to Account Management or PlayStation Store.
In case that your PlayStation 4 is activated as your Primary system, and that you’ve logged into your SEN account recently, you’ll still be able to access online gameplay during the maintenance. Also, even if PlayStation 3 and PlayStation Vita owners may have some problems with the PSN, they will be able to access online gameplay too, but of course with the same conditions mentioned before.
Source: PlayStation Forum