Joe Rossignol, writing for MacRumors:
Apple has updated its System Status page to indicate that its online store will be “updated and unavailable” due to “maintenance” tomorrow, Tuesday, March 21, between midnight and 5:30 a.m. Pacific Time (or the equivalent in other time zones, such as between 3:00 a.m. and 8:30 a.m. Eastern Time).
The timing of the downtime will naturally stir speculation given that Apple is rumored to launch new products as early as this week. Moreover, Apple commonly issues press releases at 8:30 a.m. Eastern Time, which is exactly when the so-called “maintenance” update is scheduled to be completed.
This maintenance could be nothing of interesting. But, if Apple was releasing new products in a press release tomorrow, I think minor iPad and iMac updates are the most likely announcements.