We have a situation where the regular hours of a company are 8 am - 8 pm.  I have set up the different SLAs and associated them to the appropriate entitlements using the standard business hours.  The tricky part is that they offer these clients after hours service and what happens is they will double the first response time if a request comes in after hours.  

Here is an example

Priority Level = Critical 

Case received between 8:00 AM - 8:00 PM Response time 2 hours

Priority Level = Critical 

Case received 9:00 PM - Response time 4 hours

My question is how can I have the system double the response time because the request was generated after hours? 

Thank you in Advance,