The Playstation Blog has posted a notice for PSN maintenance:
In order to continue bringing you the best online games experience on PSN, we will perform routine maintenance beginning the morning of Tuesday, June 25th. This maintenance will start at approximately 9:30AM PT (10:30AM MT / 11:30AM CT / 12:30 PM ET) and will last until around 4:00PM PT (5:00PM MT / 6:00PM CT / 7:00PM ET). During the maintenance period, you may receive a maintenance notification when attempting to access PSN.
The PlayStation Store, PlayStation Home and Account Management will not be available during the maintenance period but you will be able to access online play and apps provided that you have signed in to the Network at some point between now and the time of the maintenance. So please be sure to sign in now if you wish to access the PlayStation Network during Tuesday’s maintenance window.
What this means is that if you want to be able to play online games during this time frame, make sure to log on to the PSN right now so they can log your system for access. If you don’t then you will have to wait until 4pm PDT tomorrow (and hopefully not longer).