I believe there's a fundamental difference between, say, calling a store two minutes to closing time, or going to a restaurant 10 minutes before COB, and calling a call center, especially a tech support related one. The entire point is taking phone calls.
In a store, or a restaurant, there are other things to do after all the customers have gone home. There's a kitchen to be cleaned, inventory to be restocked, registers to cash out, and none of that can happen until after "closing". That sort of thing simply doesn't exist in a call center environment. You may have an email to send or a ticket to fill out, but by and large the emails are sent and tickets created throughout the course of the day or even during the customer's call. There's not a whole other set of work that can't start happening until all customers are gone.