AWS Certified Solutions Architect Associate Test 4

Snapshots occur asynchronously; the point-in-time snapshot is created immediately, but the status ofthe snapshot is pending until the snapshot is complete (when all of the modified blocks have beentransferred to Amazon S3), which can take several hours for large initial snapshots or subsequentsnapshots where many blocks have changed. While it is completing, an in-progress snapshot is notaffected by ongoing reads and writes to the volume.
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-creating-snapshot.html