I'm a nurse and did the academic test. I failed the first time as I only managed to score a 6 on the reading section. I practiced for about a week before but think nerves got the best of me on the day. I re sat the test and got 9 listening, 8 reading, 7 writing and 8.5 speaking.
For me the hardest section was reading, time is against you on this one. Practice skim reading and highlighting key names and points. In my test I found the questions were centered around comparing different researchers findings, because I had underlines the names I was able to find them in the text quicker, saving time answering the questions.
If you're doing the general test then an hour or two practice is fine but the academic one is much tougher and I would suggest at least a couple of hours a day for week. I bought an IELTS test book with the listening cd, really boring to listen to but it's set out exactly the same as the one on the real test.
Good luck with it