At first I took the first couple tests without being timed to get a feel for the passages and questions. Then in the middle of my practice I started separating my practice into a few passages a day. The last month or so I've been doing the last few tests under strict timed conditions. I think it depends on what you're comfortable with and how far into your studying you are. I think the closer you are to your test the more strict you should be with timing and practice.