When did Bitcoin reach its highest price on 2013/4/29?
time that a coin reaches its highest price refers to time_high; on 2013/4/29 refers to date = '2013-04-29'
SELECT T2.time_high FROM coins AS T1 INNER JOIN historical AS T2 ON T1.id = T2.coin_id WHERE T2.date = '2013-04-29' AND T1.name = 'Bitcoin'