#1 - Sept. 12, 2014, 10:09 p.m.
Once the zone is open, Nexus-Lord Donjon Rade (in Stormwind, Orgrimmar, Shattrath, Dalaran, Vale Shrines, or your garrison) will have a chat option to teleport you into Highmaul. Assemble your group, set the raid difficulty to Mythic, and then use that option to enter.
Uploading and linking to a log parse at Warcraft Logs, or any similar site that can handle 6.0 logs, would also be quite helpful.