Lead Response Time
The average time it takes a salesperson to respond to a potential customer who has contacted the company by calling, submitting an inquiry form, or sending an email.
The graphic below contains a chart from a study conducted by HBR on a group of 2,000 American companies. It clearly shows a correlation between waiting time for contact and the effectiveness of sales activities. Nearly one in four companies in the ranking does not respond to inquiries directed directly by customers.

Citing a study prepared by Insidesales together with Harvard Business Review, the longer the response time to a customer inquiry, the lower the chance of a successful conclusion to the sales process. According to the information on the infographic, contacting the customer within the first 5 minutes increases the chance of a sale by as much as 10 times, compared to contact made after 10 minutes.
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Useful links:
https://www.ringdna.com/inside-sales-glossary/what-is-lead-response-time
https://www.geckoboard.com/learn/kpi-examples/sales-kpis/lead-response-time/