This article has some good info about preparing for the RoS launch.
Reaper of Souls Launch Day PreparationCouples points:
Regional Launch Times
Reaper of Souls will launch at different times in each Diablo III gameplay region. Please see the below list to learn when the expansion will be available in your preferred region.
For Asia, the expansion will be available to play at 11:00 a.m. PDT on March 24.
3:00 a.m. KST on March 25
2:00 a.m. CST on March 25
For Europe, the expansion will be available to play at 4:00 p.m. PDT on March 24.
23:00 GMT on March 24
00:00 CET on March 25
01:00 EET on March 25
03:00 MSK on March 25
For the Americas, the expansion will be available to play at 9:00 p.m. PDT on March 24.
10:00 p.m. MDT on March 24
11:00 p.m. CDT on March 24
12:00 a.m. EDT on March 25
1:00 a.m. ADT on March 25
1:30 a.m. NDT on March 25
12:00 p.m. SGT on March 25
3:00 p.m. AEDT on March 25
Launch Night Login
Diablo III will be available the night Reaper of Souls goes live and there will be no need to patch or exit the game once the clock strikes GO!
We advise logging in ahead of time to reduce potential queue times.
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