Blizzard thinks that they’ve solved the lag issues for the opening of Ahn’Qiraj event in WoW Classic

The Calendar
First and foremost, we have the exact time of the content unlock. This will occur with the weekly raid reset in each region, because the content involves Blackwing Lair. In this region, the content will unlock on:

• July 28 at 9:00 a.m. PDT / 12:00 Noon EDT
• July 29 at 2:00 a.m. AEST / 4:00 a.m. NZST

This is the time when the War Effort will begin and each faction can turn in immense amounts of supplies that, once completed, will require five days to be transported to Silithus. Due to the raid requirements in the quest chain leading up to the “Bang A Gong!” quest, the earliest that the gong-ringing can occur in Silithus on highly-motivated realms will be just over a week later.

Once the gong is rung on a realm, the 10 Hour War begins. Once the 10 hours has elapsed, “Bang a Gong!” can never be turned in anymore, the two Ahn’Qiraj raids will open, and the “Treasures of the Timeless One” quest will become available.

The exact times for the ringing of the gong, and therefore the raids opening 10 hours later, will differ on every realm.

During the 10 Hour War, world bosses do not only spawn in Silithus. Resonating Crystals that spawn major enemies will appear in Tanaris, Feralas, Thousand Needles, and Barrens. This is important to know because we expect there to be an overcrowding issue in Silithus on realms whenever large groups of players all go to Silithus at the same time. While the negative effects of overcrowding can’t be eliminated, we’re taking several steps to mitigate the worst outcomes:

• Thanks to players who helped us test on the PTR in June, we can support a higher number of players in the zone than we could before.
• Those PTR tests also helped us determine the maximum number of players that can be supported before “a little laggy” became “unplayable.”
• If the maximum is reached, players will be automatically removed from the zone.
  • First, players will be removed if they are below level 60. Alliance players will be ported to Westfall, and Horde players will be ported to The Barrens.
  • Level 60 players who are ported out will be moved to to Un’goro Crater, Tanaris, Thousand Needles, or The Barrens.
  • If Silithus is at max population, a level 60 player can only zone in when another player leaves Silithus.
  • Players who have a Scepter will never be automatically removed from Silithus.
• Zone maximums and automatic adjustments are per-layer.

There are restrictions on realm-to-realm character transfers, which are in place to prevent players of a different realm from coming to your realm and disrupting the progress of events. The quest “Bang a Gong!” cannot be completed by characters who transferred to the realm in the past 90 days, however, those players can complete “Treasures of the Timeless One”. Before the end of the 10 Hour War on a realm, there are also other restrictions on transfers for characters who have participated in significant event activities elsewhere. For example, players cannot transfer a character that has Silithus Carapace Fragments in their bags or bank.