Takes a list of the following form: [(a1, b1), (a2, b2), ...] and
    returns a string (a_mean+/-a_error, b_mean+/-b_error).

def display_timestamps_pair(time_m_2):
    """Takes a list of the following form: [(a1, b1), (a2, b2), ...] and
    returns a string (a_mean+/-a_error, b_mean+/-b_error).
    """
    if len(time_m_2) == 0:
        return '(empty)'

    time_m_2 = np.array(time_m_2)
    return '({}, {})'.format(
        display_timestamps(time_m_2[:, 0]),
        display_timestamps(time_m_2[:, 1]),
    )