code: def timeSlice(requestContext, seriesList, startSliceAt, endSliceAt='now'):
      
      results = []
      start = epoch(parseATTime(startSliceAt))
      end = epoch(parseATTime(endSliceAt))
  
      for slicedSeries in seriesList:
          slicedSeries.name = 'timeSlice(%s, %s, %s)' % (slicedSeries.name,
                                                         int(start), int(end))
          curr = epoch(requestContext["startTime"])
          for i, v in enumerate(slicedSeries):
              if v is None or curr < start or curr > end:
                  slicedSeries[i] = None
              curr += slicedSeries.step
          results.append(slicedSeries)
      return results
docs: Takes one metric or a wildcard metric, followed by a quoted
      string with the time to start the line and another quoted string
      with the time to end the line. The start and end times are
      inclusive. See ``from / until`` in the render api for examples of
      time formats.
  
      Useful for filtering out a part of a series of data from a wider
      range of data.
  
      Example::
  
          &target=timeSlice(network.core.port1,"00:00 20140101","11:59 20140630")
          &target=timeSlice(network.core.port1,"12:00 20140630","now")