```python
import pandas as pd
import matplotlib.pyplot as plt # modify title and ylabel
df = pd.read_excel('source.xlsx', parse_dates=[2,3,4])
# aggreatge over a period: M (monthly)
df['month'] = df.set_index('timestamp').index.to_period('M')
df.boxplot(
column='targetValue', by='month', rot=90,
showfliers=False, figsize=(10,6)
)
# modify title and ylabel
plt.title("Monthly Boxplots of targetValue")
plt.ylabel("targetValueMeasure")
plt.suptitle("") # remove pandas title
plt.show()
```