Time spent at each of the case stages of SLA excluding holidays and weekend off

Hi,

I need suggestion for below requirement.

I created 4 different SLA as per business requirement. I assigned the respective SLA dynamically  based on my case type. Service calendar and holiday list configured because the organization is working for 5 days in a week   8 hours per day with 1 hour lunch  break. Suppose the business process flow having four stages , each stages need to be for 2 days SLA. I need to capture the actual time spent at each of the case stages excluding holidays and weekend off. Please suggest how we can achieve using Microsoft dynamic CRM 2015.