I think you should be able to get it in the same day. I have no experience at Houston, but the reason I am saying is because, I got my VISA the same day at the Dallas Camp.
Thanks Rama Bashyam,
What is the Dallas "camp"? Where can I find out more details about this - or can you give them to me?
Dallas is closer to me than Houston, so, depending on your answer, I could probably go there instead.