We are planning for a scheduled maintenance during that time. We are planning to create a full backup before running a script that will check the database for duplicated usernames after identifying issues that allowed users to register with a taken name.
Users that registered with a duplicated name first get to keep the name, while the other users will have their name reset. We are very sorry for this.
We are not sure how long it will take, so we are overestimating the duration by a lot.