Time slicing in Oracle/SQL

SELECT user_name, truncate(event_time, 'YYYYMMDD HH24MI'), count(*)
FROM job_table
WHERE event_time > TO_DATE( some start date time)
AND user_name IN ( list of users to query )
GROUP BY user_name, truncate(event_time, 'YYYYMMDD HH24MI')

Alice  2008-12-16 08:00   20
Alice  2008-12-16 08:01   40

SELECT
  to_char(Times.time,'hh24:mi'),
  count(*)
FROM
  (SELECT
     time
   FROM
     dual
   WHERE
     1=2
   MODEL
     dimension by ( 0 as key )
     measures     ( sysdate -1 as time )
     rules upsert ( time[ for key from 0 to 1 increment (1/1440) ] = sysdate-1 + cv(key)) ) Times,
  job_table
WHERE
  begintime <= Times.time
AND
  endtime > Times.time
AND
  user_name = 'Alice'
GROUP BY
  Times.time
ORDER BY
  Times.time