Sony has scheduled announced another bout of PlayStation Network maintenance.The service will be offline from 4.00pm on Thursday 1st March until 7.00am the following morning. PlayStation Store (PC and Console), Home, customer account management and account registration will all be unavailable.If you're logged in at 4.00pm you will be disconnected.The announcement on the
PlayStation forum
didn't mention exactly what Sony's engineers are up to.
Source

FYI