Use of analytic function

Question

I'm trying to sort a series of rows and look for the latest (based on time). I only want the latest row, because that's the one I want to update. I'm trying to figure out a query, and it looks like an analytical function is my best avenue, but the syntax is stymies me. Can someone help/suggest a correction?
select KEY_ID, to_char(START_DATETIME,'HH24:MI'), DESCRIPTION, FIRST_VALUE(KEY_ID)
  OVER (PARTITION by KEY_ID ORDER BY START_DATETIME DESC) LIST
        from TS_TIMECARD_DETAIL
       where TIMECARD_ID = 60412
       order by START_DATETIME DESC
/Thanks.
PS. Key_ID is unique/primary key.

Answer 1

That was close enough. It's actually part of a trigger designed to match up pickup and delivery information. Here's what I finally came up with:
select KEY_ID, DESCRIPTION into x_key, x_desc
        from (select KEY_ID, DESCRIPTION, START_DATETIME, MAX(START_DATETIME)
                OVER (PARTITION by KEY_ID) MAX_START_DATETIME
                from TS_TIMECARD_DETAIL
               where TIMECARD_ID = x_tc
                 and START_DATETIME < v_dttm
               order by START_DATETIME DESC)
       WHERE rownum = 1;