Daelo, our cloth-wrapped lead encounter designer, has just posted the schedule for which bosses will be tested in Ulduar on the 3.1 PTR this week. As you may be aware, they're not opening all bosses for testing at once (at least, not yet), and bosses are up only during certain hours, to let the devs watch players (try to) beat them.

This week, here's the schedule for the North American realms:

• Tonight, Tuesday 3/3, starting at 4 PM PST now: Flame Leviathan, the (in-)famous vehicle boss. Only the 10-man version should be tested, as the 25-man one is "not properly tuned." I'm really curious to see how this fight is going to work out.
• Wednesday, 3/4, starting at 4 PM PST: Ignis the Furnace Maker.
• Thursday, 3/5, starting 4 PM PST: Hodir.

And for the European realms:

• Wednesday, 4/3, 1 AM CET: Flame Leviathan, 10-man only.
• Thursday, 5/3, 7 PM CET: Thorim.
• Friday, 6/3, 7 PM CET: Freya.

Thorim on Thursday, Freya on friday? I think they did that on purpose. Daelo also promises that General Vezax and Razorscale will be soon available for European testers, and XT-002 Deconstructor for US testers.