If your question is – Is the answer time that I need to take into consideration to calculate the revenue?
The answer is YES
BUT this isn’t the only money flow to your company. It may have flat rates for subscription plans, every single plan may has conversation time included in its price. Many operators starts charging with a fixed price for the first minute or so, and after that the charging is for every second. Every subscripion plan may has different charging rates and so on.
But walking your way you can find are your company growing or shrinking?