user: Question: On what date is there a score1 of 2 - 4 with the opponent Chelsea Under 18s?
Columns: ['Match', 'Date', 'Competition or tour', 'Ground', 'Opponent', 'Score1']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1.0, '23 August 2008', 'Premier Academy League', 'H', 'Manchester United Under 18s', '0 - 0']
SQL:

assistant: SELECT "Date" FROM "Table" WHERE "Score1" = '2 - 4' AND "Opponent" = 'Chelsea Under 18s';