In a post on their official PlayStation blog, Sony's PlayStation Digital Platforms Community Manager Paul Sullivan wrote that the PlayStation Network would be going down for routine maintenance tomorrow, June 25th, for approximately six and a half hours.
The post states;
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.
Routine maintenance is a necessity of keeping networks running smoothly and something with which we should all be familiar. Just make sure to log in prior if you want to play games during that period.