I'd recommend using Date processor | Elasticsearch Guide [master] | Elastic to convert the cisco timestamps to date type. Then you should be able to use it as a sort in a data view. Or by default it will write to @timestamp which might fit your needs.
If you still want to time the log was written to ES you can use a set processor for that as shown on Event Fields | Elastic Common Schema (ECS) Reference [8.3] | Elastic