Blizzard: S3 ends on August 23rd, and S4 is scheduled to start on August 28th - which means Patch 2.3 is likely to hit in between those days.
Season 3 will be ending at the following dates and times for each region:
North America: Sunday, August 23 @ 5:00 p.m. PDT
Europe: Sunday, August 23 @ 5:00 p.m. CEST
Asia: Sunday, August 23 @ 5:00 p.m. KST
Season 4 will be starting shortly after at the following dates and times for each region:
North America: Friday, August 28 @ 5:00 p.m. PDT
Europe: Friday, August 28 @ 5:00 p.m. CEST
Asia: Friday, August 28 @ 5:00 p.m. KST