Raid timers are the technique implemented by Blizzard to prevent members of large guilds from visiting high-end instances over and over to repeatedly farm bosses in a short period of time. Despite the name a similar system also affects heroic dungeons.
Players re-entering an instance will find that bosses killed in previous visits to the same instance stay killed until the timer resets. The other implication is that the players associated with the instance have a time limit in which to complete their activities before the instance is reset. This time can be extended (from Patch 3.2.0) with the Instance Lock Extension feature.
Flexible Raid Locks
Patch 4.0.1 introduced a redesigned lockout system called Flexible Raid Locks. Raid IDs in Wrath of the Lich King and Cataclysm raids work on a per-character basis. For example, if you defeat the first two bosses of a raid instance in 25-man mode, you can call it a day and all the individual raid members can return later with any variety of 10-man or 25-man groups to do the remaining bosses (if they do it before the weekly reset).
The raid IDs are associated with individual characters; however, only the raid leader's lockout is considered in a raid group. If you have not killed any of the bosses that are available in the leader's lockout, then you may join his raid; however, if you have defeated bosses that he has not, then you will be unable to enter the instance.
On Normal mode lockouts, if you join someone else's raid in progress, you will be saved once when a boss is defeated. Even on a fresh lockout, you can join your friends in downing the last boss in a raid instance, but once any boss is defeated, you will be saved to all previously defeated bosses in the lockout. You are free to switch between 10 and 25 player difficulties on Normal mode lockouts for any boss.
If the raid difficulty is set to Heroic, then characters will be locked to the raid instance and size 'immediately' after zoning in (you are presented with a warning allowing you to leave if you do not wish to accept the lockout). The lockout will then read "Heroic (10 player)" or "Heroic (25 player)" respectively, and you will be unable to join a raid of a different size. However, you may still switch between normal mode and heroic mode for your lockout; however, no matter which mode you are currently on, players will be locked instantaneously if the 'lockout' is flagged as Heroic.
An explanation of the 4.0.1 raid lockout rules by Bashiok: http://blue.mmo-champion.com/topic/22056/flexible-raid-lock-system-in-401
Since Patch 1.9.0, instances are reset according to a fixed calendar. This was decided by Blizzard to be fairest to most and replaces the previous system of resetting raid instances based on the absence from the instance of the raid members.
Unless a raid has been extended, the following is a list of when each raid is reset:
- Molten Core: Every Tuesday at 11:59 AM
- Blackwing Lair: Every Tuesday at 11:59 AM
- Ruins of Ahn'Qiraj: Every 3 days at 11:59 AM
- Temple of Ahn'Qiraj: Every Tuesday at 11:59 AM
Burning Crusade raids
- Karazhan: Every Tuesday at 11:59 AM
- Gruul’s Lair: Every Tuesday at 11:59 AM
- Magtheridon: Every Tuesday at 11:59 AM
- Tempest Keep: The Eye: Every Tuesday at 11:59 AM
- Coilfang Reservoir: Serpentshrine Cavern: Every Tuesday at 11:59 AM
- CoT: Battle for Mount Hyjal: Every Tuesday at 11:59 AM
- Black Temple: Every Tuesday at 11:59 AM
- Sunwell Plateau:: Every Tuesday at 11:59 AM
Wrath of the Lich King raids
- Naxxramas: Every Tuesday at 3:00AM or during weekly maintenance
- Obsidian Sanctum: Every Tuesday at 3:00AM or during weekly maintenance
- Vault of Archavon: Every Tuesday at 3:00AM or during weekly maintenance
- Ulduar: Every Tuesday at 3:00AM or during weekly maintenance
- Trial of the Crusader: Every Tuesday at 3:00AM or during weekly maintenance
- Onyxia's Lair: Every Tuesday at 3:00AM or during weekly maintenance
- Icecrown Citadel: Every Tuesday at 3:00AM or during weekly maintenance
All Cataclysm raids reset at the same time: Tuesdays at 11:59 AM
- Patch 1.9.0 (2006-01-03):
- The raid-lockout system has undergone a significant change. The new system will have all instances reset at a certain server time, regardless of when you were actually saved to the instance. The reset schedule is as follows:
- Molten Core: Every 7 Days, resetting during weekly maintenance.
- Blackwing Lair: Every 7 Days, resetting during weekly maintenance
- Onyxia: Every 5 Days
- Zul'Gurub: Every 3 Days
- Temple of Ahn'Qiraj (40-man): Every 7 Days, resetting during weekly maintenance
- Ruins of Ahn'Qiraj (20-man): Every 3 Days
- All resets will occur during off-hours, when the least amount of raids are active.
- Patch 1.3.0 (2005-03-07):
- "Raid lockout" is fixed. If the leader of your raid group is saved in a different instance than you would otherwise go to, you are added to your leader's instance.
- Added /raidinfo command showing remaining time on saved raid instances. Also shows an ID to compare with other players (if you have the same saved ID as them, you will go into the same instance)
- Added a chat window message when you are first saved to an instance.