How to find the visitor who visited the White House each month?

Hello,
I am trying to figure out the visitor who spent the highest amount of time in the WH. However, there are several visitor with multiples entries in the potus_visitors.csv. Please, How can I can iterate over the data set to compute the appt_length of each visitor in one month?

Thanks
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First, share what you have tried so far. Then we can focus on where exactly you are stuck.

Hello @the_doctor ,

Here is what I has tried so far as required

My Jupyter notebook :

** My Jupyter file**
Potus_visitors_2015.ipynb (27.9 KB)

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