master item for a nested If statement based on days range

[Newgirl]

Hi Community,

Having some difficulty using an expression for a master dimension. 

Essentially it's a 2 part problem.

1. calculating the total days between 2 dates (a request and approval date)

2. then have the date ranges populate as a category based on the total of days. The ranges are as below

0-1 days 

2-4 days

5-8 days

9-14 days

etc.

How can I write the nested if statements for days 0 -1 = "0-1 Days", days 2-4 = "2-4 days" etc.

I have already tried the suggestion from the https://community.qlik.com/t5/New-to-Qlik-Sense/Nested-IF-Statements/td-p/1022597 

I have also seen that it's not possible to use a master item in another master item as I had already created the Master measure for Networkdays(Request date, approved date) renamed as "pending days", hoping to piggy back off the existing master item to create the new dimension to be something like:

if(Pending days >=2, '0-1 days', 'unknown') but it wont register the master item in the expression. 

The end result is to be able to use the groupings dimension in a pie chart to show the break down via the day grouping lengths.

Thanks