I have not had any cauliflower that will hold past maturity at all. But I live in a warm climate. I tie up the heads as soon I see the buton ( beginning of a head). They usually reach full size in a bout a week. Check the larger heads at about 5 days and every other day there after. You should have a smooth curd. When they reach maturity, you will see formations like grains of rice, still edible not prime. Any further and the individual flower stems will began to seperate.They head fast and they tend be very uniform in heading. Size depends a lot on growing conditions. If they reach x size and quit growing, no point in waiting for them to grow more. Whatever they will do, they will do swiftly.