Corrello's Cycle Time Chart shows how long individual cards took to complete vs the day they were completed on. Selecting a point on the chart lets you see how long the card spent in each part in your process.
Once you've told Corrello which lists cards are moved to when work starts on them and which lists cards are moved to when they are completed Corrello loads a history of your Trello boards for you and calculates your Cycle Time stats. You can change the date range for your chart to focus on a specific period in the history. Corrello also shows you the 50%, 85% and 95% Cycle Time percentile ranges for the date range you select.