Set TTL for documents

I want to set TTL (time to live) at couchbase server for all documents getting pushed from mobile devices continuously for replication. I did not find any clear explanation/example in documentation to do this. Could you please let me know the exact way to do this?
Also what is the way to set TTL for only specific documents?

Should I do it by using webhooks where it will listen to document changes (creations) made through Couchbase Lite push replications, set TTL for new documents and save back to Couchbase server?
Is there any other better way to do it?