def estimate_reasonable_max(df, x):
    """Estimate a reasonable maximum value for the plot y axis."""
    # Use 1.5 IQR of the largest group.
    group = df.groupby(x)
    q1 = group.Time.quantile(0.25)
    q3 = group.Time.quantile(0.75)
    iqr = (q3 - q1).max()
    return q3.max() + 1.5*iqr