Sony Computer Entertainment America and Sony Computer Entertainment Europe have confirmed that the PlayStation Network will be taken offline for routine maintenance on Tuesday, June 25, 2013.
While the PlayStation Store, PlayStation Home and Account Management features will be inaccessible during the maintenance period, users will still be able to play online and access applications as long as they signing into the PSN before the maintenance kicks-in.
The maintenance will start at approximately 9:30AM PT (10:30AM MT / 11:30AM CT / 12:30 PM ET/5.30pm BST) and will last for approximately 6 and half hours coming back online around 4:00PM PT.
So, if you want to be able to play online during this time, you must remember to sign in before it begins.