If you already have a test appointment, try taking your CAT's at around the same time. If it's an 8am appointment, take a test once every week or so on the weekend, but at 8am. Only then will you be able to gauge your concentration level that early in the day. I can't see how you can focus to the best of your ability if you are taking tests at 8pm on a work day!
Once you schedule your test appointment, make sure you adjust your waking schedule a few days before the actual test so that you're used to getting up at 6am etc. if your test appointment is at 8am. A lot of people end up sleeping only 4-5 hours the before the test because of stress, changed sleeping patterns etc. and do significantly worse that expected by the time they reach the Verbal section.
My advice would also be to avoid caffeine so that you don't have to go through a "crash" 2 hours into the test.