How long does the fertile window last?

C

For the first time in 6 months I'm actually ovulating based on the Clear Blue Advanced ovulation test. I've had a high result on cycle days 15, 16, and 17. How soon until I'm estimated to peak? Glow says I'll peak on the 12th, but I have 21 day bloodwork scheduled with my doctor on the 12th to confirm ovulation. So I'm a bit confused. What if I haven't ovulated by then?