MediaWiki:Apihelp-query+readinglists-param-changedsince/en

Show lists that have been changed since this timestamp. Must be after $1. Clients should use the timestamp returned in the readinglists-synctimestamp field from an earlier call if they want to ensure that no changes are missed, and should be prepared to receive changes that have already been returned in an earlier response, and handle them in an idempotent way.