Create a stand-in screen or page (depending on whether the system is client-server or http-saas) which tells the user how long the system will be down. In our c-s systems we swap the real main executable with a stand-in executable that displays, for instance, "System down for maintenance and will return at 1200 Pacific." The stand-in executable reads a text file which we can edit to change the time and certain other information. In one of our systems, the database update DDL is contained in a text file. In another system, the DDL is in-line, with product code. I'm not sure how you might give the user an actual real-time, accurate status on the update. The database update process might maintain a field in the database which would contain a progress number and would be read periodically by the stand-in page or executable. I've found that users are satisfied just knowing approximately when their system will be available again.