Performing a database repair is a more exhaustive check of the internal database structure, and so more time is required for each table compared to a simple health check. If a Database Health Check has not yet been performed since the QubeGUI has been started, there is no way to know which (if any) databases contain tables with errors, so all tables in all databases must be scanned.
It is usually quicker to first run a Database Health Check to find tables with errors, and then run the Database Repair to fix only the tables that need repairs.
A first pass at a repair attempt is done in a relatively quick manner that catches all but the most egregious of error conditions. If this first repair pass fails, a second more exhaustive repair is attempted which involves rebuilding all the table indices by performing a full table scan. (The mysqlcheck "–use-frm" option is used.)