user: Question: When did the old manager vacate his position in Plymouth Argyle?
Columns: ['Team', 'Outgoing manager', 'Manner of departure', 'Date of vacancy', 'Replaced by', 'Date of appointment', 'Position in table']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Crystal Palace', 'Peter Taylor', 'Contract terminated', '8 October 2007', 'Neil Warnock', '11 October 2007', '19th']
SQL:

assistant: SELECT "Date of vacancy" FROM "Table" WHERE "Team" = 'Plymouth Argyle';