Cash Express (Zamnesia) - Beginner 1st Time Grow

Either way is fine, it's your diary. I personally like to wait until my tops show obvious signs of transition to flower. I feel things like breeder flowering estimates tend to be a little closer to accurate this way. If your looking for a concensus answer, most growers on here do it at their light change.

Now that she is in flower, she is starving for potassium and phosphorous too. According to your diary, you have not used any fertilizers at all, the yellow is a sign of multiple deficiencies..........especially nitrogen and no douby, many minor nutrients, like magnesium.