DATA: l_start TYPE t,
        l_end TYPE t,
        l_startdate TYPE d,
        l_enddate TYPE d,
        l_hours TYPE p DECIMALS 2.

  l_start = p_starttime.
  l_end = p_endtime.
  l_startdate = p_startdate.
  l_enddate = p_enddate.

  l_hours = ( ( l_enddate - l_startdate ) * 24
             + ( l_end - l_start ) / 3600 ).