It all depends on how your body responds hormonally. Some people know within a day, just from one symptom (like having cravings), and others don't have a craving till 2nd tri. I'd say it could be a good sign, but a lot of people have cravings just from when ovulation happens. If it's not in the range of "normal" for you, I'd say test within a week of expecting AF. Of course, I'm not the pro on these things, cause I hardly keep track of AF myself, but the cravings could be it...