how to calculate business days in the incident level

Summary

Based on the business days, in My Inbox report level, the record colour needs to be changed. For example, once the incident is created for the **** category. For the **** category, the resolution for the category is 10 business days. After 5 business days, the record colour changed to "Amber" and after 9 business days the record colour changed to Red. How to achieve this functionality in the My Inbox Report

Content (please ensure you mask any confidential information):

Based on the business days, in My Inbox report level, the record colour needs to be changed. For example, once the incident is created for the **** category. For the **** category, the resolution for the category is 10 business days. After 5 business days, the record colour changed to "Amber" and after 9 business days the record colour changed to Red. How to achieve this functionality in the My Inbox Report