user: Question: What is the number of rounds that took place for the fight that lasted 6:21?
Columns: ['Res.', 'Record', 'Opponent', 'Method', 'Event', 'Round', 'Time', 'Location']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text', 'text']
Sample row: ['Loss', '34–9 (1)', 'Diego Sanchez', 'Decision (split)', 'UFC on Fuel TV: Silva vs. Stann', 3.0, '5:00', 'Saitama , Japan']
SQL:

assistant: SELECT "Round" FROM "Table" WHERE "Time" = '6:21';