Hi!
At 17:00 UTC (10am PST, 1pm EST, 19:00CEST) we will start the process of our schema change release. The exact time that we plan to start the change will depend on how long it takes to finish our preparations, but we expect it to be shortly after 17:00UTC.
Once we start the process we will put a banner notification on musicbrainz.org and we will also post updates to the @MusicBrainz twitter account, so follow us there for more details.
After the release is complete, we will post instructions here on how to upgrade your replicated MusicBrainz instances.
MetaBrainz Blog 