The <uniqueVersion> configuration applied to artifacts that were deployed (via mvn deploy) to a Maven repository such as Nexus.
To remove these from Nexus, you can easily create an automated job to purge the SNAPSHOT repository every day. It can be configured to retain a certain number of shapshots or keep them for a certain period of time. Its super easy and works great.
Artifacts in the local repository on a developer machine get there from the “install” goal and do not use these timestamps…they just keep replacing the one and only SNAPSHOT version unless you are also incrementing the revision number (e.g. 1.0.0-SNAPSHOT to 1.0.1-SNAPSHOT).