It appears the original announcement regarding tonight's PlayStation Network was way off. Originally announced to last nine hours, Sony has clarified that the maintenance will only last two hours.
It is now scheduled to start tonight, Monday, May 11, at 9:00pm PDT (Tuesday, May 12, 12:00am EDT), and expected to end on Monday, May 11, at 11:00pm PDT (Tuesday, May 12, 3:00am EDT). Much better than the originally announced nine hour period.
During this time, you may experience issues with Account Management, PlayStation Video, and PlayStation Store, but you should still be able to play games online as long as you've signed into your account (within the past 24 hours on PS4) beforehand.
"During maintenance, online gameplay is available on your PlayStation system if you have recently signed into your account on it (within past 24 hours for PS4). Make sure you sign in on the PlayStation systems that you might want to play online with before the maintenance begins," Sony says.
"We endeavour to ensure that PlayStation Network services are available at all times. However, occasionally Sony Entertainment Network may need to be taken offline so we can perform essential maintenance. This is to ensure our network continues to run smoothly and securely and to provide you with new and updated services."