The maintenance is scheduled to begin on Tuesday, June 16th at 12:01 AM (PST) and will last for an undetermined amount of time. While it may just be playing it safe, Microsoft has announced that the maintenance could take as long as 24 hours. Let’s hope it doesn’t come to that.
The “My Xbox” area of Xbox.com will also join LIVE for an offline siesta, and the Xbox forums will be in read only mode. So take a few hours and get to know your family again, catch up with some old friends, or play with your pets. Who knows? You might even meet someone to play some offline multiplayer with.
Source: Major Nelson