Update May 21st: This maintenance window has been postponed.
On May 15th, Linden Lab gave warning that there will be a period of scheduled maintenance on Thursday May 22nd which will see log-ins suspended for around one hour, from approximately 07:00 SLT.
The notice, posted to the Second Life Grid Status Page reads in full:
[Posted 2:15 PM PDT, 15 May 2014] The Second Life Service will be closed for logins for approximately one hour on Thursday, 22 May beginning at 7am PDT.
Residents in world will not be logged out, but will experience loss of supporting services such as search and inventory. New logins will not be accepted, and Residents in world should not attempt to transfer or manipulate L$ or valuable (no-copy) assets until the ALL CLEAR is given.
As always, if the scope or the schedule of the work changes, we will update this post.
Please bear the above in mind, and keep an eye on the Grid Status Page for updates on this announcement,