Activity Plans have the capability to implement Business Days when calculating target dates for activities. This option settings allow your organization to define where Business Hours are defined by your organization. 

• For Matter based Activity Plans, business hours can be derived from:
  
  
  1. Matter Court
     Use the business hours assigned to the Court entity.
     
     
  2. Organization Default
     Use your organizations default business hours.
     
     
  3. Business Hours Lookup
     Use the specified custom Business Hours lookup field from the Matter object.
     
     
• For Account and Contact based Activity Plans, business hours can be derived from:
  
  
  1. Organization Default
     Use your organizations default business hours.
     
     
  2. Business Hours Lookup
     Use the specified custom Business Hours lookup field from the Account or Contact object.