I spent a month (just under 30 days) preparing for my TEAS test. I studied between 2 and 3 hours every day, and the last week before my exam, I studied a bit more (about 4 hours a day), because I have been out of school for some time (I am a returning student, and got my first bachelor's degree in 2007, so it had been quite a while since I've done the math and science!). I found that studying for a month was just right; by the time my test came around I felt fully prepared, and felt that if I had kept on studying, it would have been more of a hinderance than a help, because I needed to just get the test over with. I was pleased with my overall score (I got an 86, which for my school was actually pretty high, as the average of accepted students for my school is 73). I was aiming a little higher (I wanted to break 90), but I was pleased. Most people I have talked to have also said that they studied for a month, and felt it was just the right amount of time.
After having taken it, I would definitely say that studying for over a month would just be overkill. But I would also advise not to study for too much less than that, even right out of school.
Also--don't be anxious! I went through that myself--it's such long process, and can DEFINITELY wear on the nerves. But just remind yourself to take deep breaths and not let nerves get in the way, especially while you are studying. I can't tell you how many times I would sit there while studying and get totally overwhelmed and an hour would have gone by and I got nothing done! The time and effort you put in now will pay off, and you will find that you really have nothing to be anxious about
Hope this helps!