Error is:

Report execution failed: ERROR: invalid input syntax for type timestamp: "" 

Report SQL is:

SELECT id as ticket, summary, component, c.value as location, t.type AS type,
   status, time AS created
FROM ticket t
  LEFT OUTER JOIN ticket_custom c ON (t.id = c.ticket AND c.name = 'location')
WHERE t.time BETWEEN EXTRACT(EPOCH FROM TIMESTAMP '$START 00:00:00') AND EXTRACT(EPOCH FROM TIMESTAMP '$END 23:59:59')
ORDER BY time ASC, location, type