Expect the store to be inaccessible between 8:00AM PT to 8:00PM PT.
As part of normal practice for Sony's PlayStation Network, the PlayStation Store and Account Management will not be accessible from Thursday morning to Thursday evening due to scheduled maintenance.
Downloaded content, network play, and services such as Netflix should function as normal, but users should be sure to be current on any updates prior to the scheduled maintenance in order to avoid any downtime.
From the PlayStation Blog, "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."