def drop_before_index(
    index: Union[pd.RangeIndex, pd.DatetimeIndex],
    split_point: Union[int, pd.Timestamp],
) -> Union[pd.RangeIndex, pd.DatetimeIndex]:
    """
    Drops everything before the provided time `split_point` (excluded) from the index.

    Parameters
    ----------
    index
        The index to drop values from.
    split_point
        The timestamp that indicates cut-off time.

    Returns
    -------
    Union[pd.RangeIndex, pd.DatetimeIndex]
        A new index with values before `split_point` dropped.
    """
    return slice_index(index, split_point, index[-1])

    Drops everything before the provided time `split_point` (excluded) from the index.

    Parameters
    ----------
    index
        The index to drop values from.
    split_point
        The timestamp that indicates cut-off time.

    Returns
    -------
    Union[pd.RangeIndex, pd.DatetimeIndex]
        A new index with values before `split_point` dropped.
    
darts/utils/utils.py