One of the reports on the Mission Control screen is the New Lead Cohort Over Time.  The report was designed to show you how valuable your new leads are up to 90 after they are added to your list.

This report will allow you to find out how long it takes your new leads to become valuable.  If your leads don't typically buy immediately after they join your list, the New Lead Cohort Over Time report will show you how long a new leads generated from your ads should take to overcome the cost of acquiring them.

Below is a video to show you exactly how this report works.