between particular times of the day.

        Examples
        --------
        >>> i = pd.date_range('2018-04-09', periods=4, freq='2D')
        >>> ts = pd.DataFrame({'A': [1, 2, 3, 4]}, index=i)
        >>> ts
                    A
        2018-04-09  1
        2018-04-11  2
        2018-04-13  3
        2018-04-15  4

        Get the rows for the first 3 days:

        >>> ts.first('3D')
                    A
        2018-04-09  1
        2018-04-11  2

        Notice the data for 3 first calendar days were returned, not the first
        3 days observed in the dataset, and therefore data for 2018-04-13 was
        not returned.
        zqfirst is deprecated and will be removed in a future version. Please create a mask and filter using `.loc` insteadr