Convert val out of numpy time, for use in to_dict.
    Needed because of numpy bug GH#7619

def ensure_us_time_resolution(val):
    """Convert val out of numpy time, for use in to_dict.
    Needed because of numpy bug GH#7619"""
    if np.issubdtype(val.dtype, np.datetime64):
        val = val.astype('datetime64[us]')
    elif np.issubdtype(val.dtype, np.timedelta64):
        val = val.astype('timedelta64[us]')
    return val