How fast will follicles grow if i took Clomid?

I took 50mg Clomid on CDs 3-7. I went in for a ultrasound on CD 10 and I had one follicle that was 8mm and another that was 9mm. She said to came back in on CD14 to see if they grew anymore since right now they are still too small to release an egg. So I was reading that they want them to be at least 18 but more like 22mm before I take a trigger shot. I am not anywhere close to that, is it possible that they can grown that much in 4 days? Coming in only 4 days later seems early to me. My insurance covers most of this but dishing out 30 bucks for every appointment is adding up! Shouldn't I wait longer than CD14 to get tested? I thought they only grew 1 to 2 MM a day. Will the clomid allow them to grow faster?