Blizzard's already let us know the scheduled downtime for Tuesday, June 29th, quite a bit ahead of their usual late Monday night announcement time. Right now, most realms can expect a normal downtime window of 5 AM to 11 AM Pacific time on Tuesday, June 29th. However, it is time for the next batch of US servers to go down for 24 hours, from 12:01 AM, June 29th to 12:01 AM Wednesday, June 30th.
As with the first batch, the 24-hour downtime will likely be used to get the servers in shape for Cataclysm's launch, and if we're lucky, should mean less downtime in the first few days and weeks as everyone comes in to check out the new content.
Check out the full list of servers with extended downtime behind the break: