When will Riot add Patch 6.4??

Patch Notes are shown a day before the patch comes out. It will come tomorrow, early in the morning (for EST).

Yup! As Inept Maverick mentioned, the server will go down later tonight/tomorrow morning:

Network Operations – Yesterday at 11:43 AM On 02/25/16, starting at, 01:30 Pacific Time (09:30 UTC), ranked queues will be disabled in preparation for patch 6.4. At 03:00 Pacific time (11:00 UTC), the servers will be shut down and all games currently in progress will end in a draw and stats will not be recorded. We estimate the battlegrounds will be unavailable for 3 hours.

http://status.leagueoflegends.com/?en_US#na

Korea server is disabled.Now Riot adds them.