Cats really vary with when the best time to test is. Typically, your +1 number will reflect a food spike. Your +2 should be about the same as your pre-shot. However, not all cats follow the rules. If numbers start to drop early, it usually means it's going to be an active cycle. You can look at Gabby's SS. She's known for fast, early drops. (This is why I test early in the cycle. I got really tired of being surprised!)
There's a description of what an ideal curve should look like in the "New to the Group" sticky.