The Warcraft raid instance timers will be changed with Patch 1.9. Caydiem explains it all:

In 1.9, the way raid timers are handled will undergo 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 times are as follows:

* Molten Core: Every 7 Days, resetting during weekly maintenance.
* Blackwing Lair: Every 7 Days, resetting during weekly maintenance
* Temple of Ahn’Qiraj (40-man): Every 7 Days, resetting during weekly maintenance
* Onyxia: Every 5 Days
* Zul’Gurub: Every 3 Days
* Ruins of Ahn’Qiraj (20-man): Every 3 Days

The resets, if not during weekly maintenance, are planned to occur during off-hours when the least amount of raids are active. We plan on implementing a calendar of sorts on the website to help you better plan out your particular raid schedule. There are many reasons why this particular approach was chosen; we’ve gone over a multitude of options and felt that this change would be best in the long run.

As the reset time approaches (<24 hours til the reset, I believe), if you are in the instance, you will be informed of the impending reset every hour on the hour. 15 minutes before the reset, the reminders become more frequent; once the reset time is reached, all players in the instance will be ported to their bind point. You can access your saved raid status at any time via /raidinfo, and you will be informed of your status regarding an instance when you zone into the dungeon.

We know that this change is a major one for raiding guilds; we’ve done our utmost to make the reset times as convenient as possible for the majority of our players. All saved instances will be reset when 1.9 goes live to accommodate this change.

So, basically, everyone and their imaginary little brothers will be in Molten Core Tuesday night, after a brief visit to Onyxia, of course. Wednesday and Thursday will be Blackwing Lair nights, although some guilds will be doing mop up in MC, and the weekends will be Onyxia Redux. Depending on your Blackwing speed, and/or tenacity, pillage that new-fangled Temple on Thursday and Friday … add Saturday, Sunday if it’s a particularly “wipey” zone.

What was once the Sunday/Monday lag crush will become the Tuesday Disco. Hell, we won’t need a calendar for that.

(Naturally, that Temple will take priority the first few weeks — remember Foton’s golden rule of new content: get the loot while the getting’s good. Hotfixes are your enemy.)

Oh yes. I ostensibly forgot about ZulGrub and the new (also 20-man) Ruins of Somethingorother.

Our guild leaves the 20-mans for the overflow guildies that couldn’t get a spot in the MC+ runs. We’re nice like that. Outdoor dragons, same thing. “Sure, c’mon out here hunters and rogues! Ok, not you rogues, but hunters, come one, come all. You come too, priest that’s always AFK. And you too, out of combat rezzing paladin. The feral druids wouldn’t get anywhere without you!”

What are they talking about we don’t share?? That’s sharing!