On their news blog, PlayStation have announced that there will be a 12-hour window of maintenance due this Thursday.
“In order to continue bringing you the best online games experience on PSN, we will perform routine maintenance beginning the morning of Thursday, January 17th. This maintenance will start at approximately 8:00AM PT (9:00AM MT / 10:00AM CT / 11:00 AM ET) and last until around 8:00PM PT (9:00PM MT / 10:00PM CT / 11:00PM ET). During the maintenance period, you may receive a maintenance notification when attempting to access PSN.
The PlayStation Store 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 into PlayStation 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 Network during Thursday’s maintenance window.”