While we would like to implement the fix on the 18th, the time in which we would complete the fix confirmation overlaps with JP peak time, and as we would like to prioritize everyone's play time we've decided to implement the fix on the 19th.
How many maintenance windows fell in (Insert X Countries Peak Playtime Here)? Why would you delay a patch / hotfix just because it falls in Peak times for JP players when you have absolutely no problem interrupting services during peak times for other countries?