As a provider of customer service, it is not your job to define your customer's needs, but to respond to those needs. They are concerned with their own problems. The customer feels it is reasonable. Customers call when their work involves your unit. They do not want to wait.
Some customers become very dependent on units they do business with.
This is exactly what you want. Customers who feel comfortable calling you will become regulars. Keep them closed until you think a minute has elapsed, then open them. More than likely you opened your eyes before the minute was up. A minute can be a long time.