Creates a series of folders from a given starting date
OK let's look at your code.
Unused Imports
pathlib was imported but I don't see any use of it in the codebase, I understand that this might be as a result of testing out approaches to a problem. pylint can help mitigate this by catching unused modules. It also catches some PEP guidelines which your code breaks.
Avoid Globals
You have lots of global variables. A common approach whenever you want to use a global is asking yourself some questions; &quot;How do I express myself with code whilst avoiding this global variable&quot;. When in doubt,  prefer objects that holds state to global variables.
Code Review
On first glance,  I can see you are manually parsing dates. This doesn't look good, you introduce bugs when reinventing the wheel. Right now,  your code contains a bug,  it accepts invalid dates,  I can easily create a date like this
date = &quot;12-03-202022&quot;
The above code generates no error, this can be disastrous.
A common alternative is using python  datetime module. This simplify everything, we can move the dates by periods easily,  creating directories becomes quite easy.
NOTE: datetime  module checks for invalid dates.
A simple way of creating a date from a string is given as
from datetime  import datetime
date = datetime.strptime(start_date, &quot;%d/%m/%y&quot;)

This simple line of code simplifies everything,  the full code can then be written as
&quot;&quot;&quot;Directory creating program&quot;&quot;&quot;

import os
from datetime import datetime, timedelta

def next_date(date, period):
    &quot;&quot;&quot;Increase the date by timedelta
        date: datetime object
        period: timedelta to increase our date by
    &quot;&quot;&quot;
    new_date = date + timedelta(days=period)
    return '/'.join((str(new_date.day), str(new_date.month), str(new_date.year))), new_date

def make_directories(home_dir, start_date, instances, period):
    &quot;&quot;&quot;Create sub directories in the home_dir

        home_dir: base directory
        start_date: date to append to directories created
        instances: number of directories to create
        period: difference between two dates
    &quot;&quot;&quot;
    date = datetime.strptime(start_date, &quot;%d/%m/%y&quot;)

    for i in range(instances):
        start_date = start_date.replace('/', '-')
        dirpath = os.path.join(directory, start_date,'Documentation')
        try:
            os.makedirs(dirpath)
        except FileExistsError:
            print('Directory {} already exists'.format(dirpath))
        else:
            print('Directory {} created'.format(dirpath))

        start_date, date = next_date(date, period)

if __name__ == &quot;__main__&quot;:
    directory = &quot;/Users/myName/Box Sync/SAFAC/Budget Requests/2020-2021/Weekly/&quot;
    make_directories(directory, '3/1/20', 10, 5)