Copied from the PM I sent to all guild members:

Uldum is going to be undergoing extended maintenance from 12:01 AM on Tuesday, June 8th to 12:01 AM to 12:01 AM Wednesday, June 9th. Due to this, we will be unable to have a Tuesday night raid. In order to rectify this situation, Wednesday will be the new Tuesday, we will be opening up a Thursday night raid, and Friday will remain unchanged. Free for all signups are currently open for Wednesday and Friday, and Thursdays raid will open up at 6:00 server on Monday, June 7th. It will be free for all at that point. Anyone who is running a 10 man that night, we ask you to please sign up for the 25 man run. We are a 25 man guild and hope that the priority will shift to the large raid. If you have any questions, feel free to contact Ulantor or me.

Sorry for the inconvenience here, blizz kind of screwed us over.

Also to clarify.
Those who signed up for tuesday, that raid is dead. It is cancelled and signups for it are gone. Sign up for Wednesday/Friday if you want to raid those days. Thursday sign ups unlock Monday 6/8 at 6:00 server as stated. There are no priority sign ups. There will NOT be a "transfer" from Tuesday to Wednesday of anyone. If you want in night 1, sign up for Wed ASAP.

~Risu