def get_file_time(data_filename, time_col_name):
    """Return the time of an instantaneous data set.

    Read the first two rows of a data file in order to get the time.
    Expects that the normalized time is in the first data column.

    Arguments
    ---------
    data_filename : str
        Path to data file.
    time_col_name : str
        Name of column which contains time data.

    Returns
    -------
    time : float
        Value of time in first data row.
    """
    with open(data_filename) as f:
        header = f.readline()
        row1   = f.readline()

        time_col_num = header.split(',').index(time_col_name)
        time = float(row1.split(',')[time_col_num])

    return time