what is the date of the 2010-06-29t20:30:00-08:00 football match, where ricardo casas was an assistant at.
(AND soccer.football_match (AND (JOIN (R soccer.football_referee.assistant_referee_at) m.0c0mf80) (le time.event.start_date 2010-06-29T20:30:00-08:00^^http://www.w3.org/2001/XMLSchema#dateTime)))