Blizzard posted an updated testing schedule for Ulduar.

North American realms can test Flame Leviathan (Normal mode only) on March 3rd at 4PM PST (or after PTRs come back up), Ignis the Furnace Master March 4th at 4PM PST and Hodir March 5th at 4PM PST.

European realms can test test Flame Leviathan (Normal mode only) on March 4th at 1AM CET (or after PTRs come back up), Thorim on March 5th at 7PM CET and Freya on March 6th at 7PM CET.

More info after the jump!

The original post:

Here's the current schedule for Ulduar PTR testing this week:

On the North American test realms:

Flame Leviathan (Normal, i.e. 10 Player Mode ONLY) - Tuesday Night, March 3 at 4PM PST (or after the PTR servers come back up) through tomorrow. We want a lot of testing on this, but take note that the Heroic version of this fight should NOT be tested at this time. Players should only form 10 player raids to test this. The Heroic/25 Player version is not properly tuned.
Ignis the Furnace Master - Wednesday night, March 4, starting at 7pm EST/4pm PST.
Hodir - Thursday night, March 5, starting at 7pm EST/4pm PST

On the European test realms:

Flame Leviathan (Normal, i.e. 10 Player Mode ONLY) - Wednesday Morning, March 4 at 01:00 CET (or after the PTR servers come back up) through tomorrow. We want a lot of testing on this, but take note that the Heroic version of this fight should NOT be tested at this time. Players should only form 10 player raids to test this. The Heroic/25 Player version is not properly tuned.
Thorim - Thursday night, March 5, starting at 7pm CET.
Freya - Friday Night, March 6, starting at 7pm CET.

We should have General Vezax (EU), XT-002 Deconstructor (US), and Razorscale(EU) available for testing soon after this.

This schedule could change at a moment's notice due to server, bug, or patch status. I'll try to keep everyone informed as much as possible. Ulduar and the bosses to be tested will remain also open a variable length of time. How long they stay open depends upon a host of factors including designer availability, bug status, etc.

We also hope to have the zone open on off days for each respective realm for a longer period of time. We have a couple special versions of Patchwerk setup. One of them is called Patchwerk (DPS Test) and is essentially a massive training dummy for your raids. The other is Patchwerk (Tank Test), and he does not have a Hateful Strike, but his melee damage increases over time.

We're very interested in seeing combat logs and parses for all raid testing on the PTR.

Quick Ulduar FAQ:

Q) Will there be testing available on Oceanic, Korean, or other time zones?
A) There will be some testing available. Flame Leviathan will be up for an extended time, for instance.

Q) Where's all the trash?
A) We don't have everything turned on for these tests, and this sometimes includes trash creatures before each boss encounter.

Q) Where's the loot?
A) We don't have this attached to bosses yet, but we'll have loot hooked up soon.

Q) What about achievements?
A) These aren't implemented yet.

The original post by Daelo is located here.