Why business hours matter
A one-hour target sounds simple until a customer writes at 5:40 pm on a Friday. In calendar time the reply is due at 6:40 pm; in business hours with a 6 pm close it is due at 9:40 am on Monday. Both are legitimate SLAs, but your team and your customers need to know which one you mean.
Use the calculator to check a contract before you sign it, to settle whether a specific reply was on time, or to see how much a later closing time or weekend cover would change your deadlines. For how to define and report the metric, read how to measure first response time in Slack Connect.