The maintenancewill last roughly 14 hours,and during that time any functions such as online multiplayer that require the service will be unavailable for users.
"Unlike typical maintenance events, consumers who are already signed-in to PSN will be signed-out, and consumers will be unable to sign in for the duration of the maintenance window," Sony states. "During this time, users won’t be able to access the PlayStation Store, PlayStation Home, Account Management or play online."
Service will be interrupted starting at 8am Pacific on Thursday, March 1st, and run until around 10pm Pacific.
Sony did not go into specifics regarding what will be taking place during the disruption beyond the fact that it will be significant maintenance period.