Sony's PSN maintenance, which was originally planned for Monday before all the DDoS attacks over the weekend, has been rescheduled for tomorrow, Thursday, August 28. It will still take place from 9:40 am to 4:50 pm Pacific Time (12:40 pm to 7:50 pm Eastern Time) — approximately 7 hours should everything go smoothly, which I'm sure, as a PlayStation user, you're aware isn't always the case with Sony.
"During this time we will deploy a series of back-end improvements to the network," Sony explained.
If you've signed in to the network any time since August 23rd, you should still be able to play games online and access partner apps like Netflix during the maintenance period. The PlayStation Store, PlayStation Home and Account Management will not be available during this time.
As I mentioned, the maintenance was originally scheduled to take place on Monday; however, in light of a series of DDoS attacks on the PlayStation Network on Sunday (and part of Monday), Sony decided to delay. PSN has since been running smooth, but the threat of another DDoS attack remains a possibility given that Lizard Squad is still very much active. Just last night they took down League of Legends and Twitch.tv.