Configure the Allowed RODC Password Replication Group – leave the user out of that group. Then use Denied RODC Password Replication Group to explicitly deny caching for that user. (But if user is not in Allowed, their password never caches – they can only authenticate when a writable DC is reachable, which defeats the "only during maintenance window". For time-based access, you would instead use Group Policy with logon hours and ensure the RODC has the password cached only during the window.)