Absolutely! You can define your company holiday calendar as well as your weekend days in the Profile – Customer Setup screen.
So when a request is sent to a manager for approval, the due_days for that stage is calculated as follows – the difference between the current date and the date when the request reached the manager is taken. The holidays and weekends are deducted from the difference. This gives the net amount of days still remaining for this task to be completed in the manager review stage.