Sign-in before the work begins and there's a chance you'll still be able to play online.
PlayStation Network will be offline for 12 hours while essential maintenance is carried out.
The service will be inaccessible from 2pm (6am PST) today until 2am on Tuesday, April 17th (6pm PST April 16th).
During this time, users will be unable to browse or buy from the PlayStation Store on PS3 and PSP devices. Nor will you be able to access PSN Account Management or PSN Account Registration.
Sony says that if you log-in to the service before the maintenance begins, you might be able to continue playing games online during the downtime. But it gave no guarantees.
Any trophies unlocked during the maintenance will, of course, be added to your profile once the service is back up and running.