The latest sizable batch of realms slated for the Connected Realms feature will be going under maintenance on Monday, October 21 from 5:00 a.m. PDT until approximately 11:00 a.m. PDT, according to the official thread on the feature. Community Manager Bashiok also added that once these realms return from maintenance, the realm connections should be complete. The realms scheduled for this round of connection are as follows.
Balnazzar and Warsong
Gurubashi and Aegwynn
Dalvengyr and Dark Iron
Garithos and Chromaggus
Onyxia and Burning Blade
Maiev and Bloodscalp/Boulderfist
If you happen to be calling any of these realms home, be prepared for a brief bout of maintenance come Monday. However, Tuesday's regular maintenance should simply be a set of rolling restarts for everyone, so realms that are in the process of being connected should be hit with double downtime. This seems to be a pretty quick turnaround -- will we be seeing more realm connection announcements next week? For more information and updates on the process, keep an eye on the official forum thread.