Instructors have the option of allowing students to view the Similarity Report. If your instructor has enabled this option, then the Similarity Report for your submitted file is usually created within 5 to 10 minutes of submission. That is for an average paper of 500 to 1000 words. Longer papers will take a little more time.
However, please note that Similarity Reports for resubmitted assignments take 24-hours to regenerate. During this time, you will not have access to the Similarity Report or the similarity index (percentage). If your instructor has not allowed students to view the Similarity Report, you will need to contact your instructor regarding this matter.