You’re safe to use the volume once you have triggered the snapshot, even if it’s still in a pending state according to AWS – see this post.
If you’re taking a snapshot for the first time, it probably will take a while as it has to make a full copy to the region-wide S3 bucket, but remember, it’s incremental after the first one has been stored so should be a lot faster.
NOTE: You can’t create a volume out of a snapshot which is in a pending state. You’ll get the error “Snapshot is in invalid state” if you do this.
So please make sure to wait until the snapshot is in the “available” state.