You bring up a great question. As answered below, the time period almost without exception is calendar days. HOWEVER, in terms of getting a loan, realize that your lender may have as few as 11 business days to get you the approval you need. Be sure to discuss this with your Realtor and lender before moving forward.
If you have any questions or if I can be of service in any way, don't hesitate to get in touch.
Can do, will do,