How long did it take you to get a flat stomach?

Im 5’1 and 118 pounds. I don’t have a big belly but its not flat either. I know that in order to get a flat stomach you have to remove the layer of fat covering the belly. Im getting rid of the fat by running and doing cardio. I also do a lot of crunches for the abs to show. How many should I do per day and for how long? Thanks in advance!