On May 14th at 3:00 AM PST for NA, 5:00 UK Time for EUW and 03:00 CEST for EUNE, servers will go down for maintenance and the 5.9 patch will be applied.
"On 05/14/15, starting at, 01:30 Pacific time (08:30 UTC), ranked queues will be disabled in preparation for patch 5.9. At 03:00 Pacific time (10:00 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.."Be sure to check your particular servers status page for your region's specific 5.9 maintenance times:
I'll keep you updated as more information on what the patch contains and patch notes become available. While the [ 5.9 PBE content ] is usually a good indicator of what's to come, please remember that it is tentative and not everything may make it to live.