How many days if will take to a subcentimeter follicle to to be ready for ovulation?

5-7 days: It takes 85 days to make an egg. The sub-centimeter follicles (antral follicles) found at the onset of the menstrual cycle have started a slow maturation process towards possible ovulation a whole 70 days before the event. In the two weeks between menses and ovulation (which occurs at a follicular diameter of about 20 mm) they grow much faster, at about 2 mm per day.

Around 7 days: Every month at the start of the menstrual cycle (day 1 at the start of the menses) there are @ 1000 eggs each in a follicle cyst too small to be seen. As each day goes by, fewer cysts survive until several remain each having grown large enough to see on ultrasound but still "subcentimeter" ie millimeters. Generally only one "dominant follicle" then progresses on to a 2cm size ready to ovulate.