When you move a card to your to do list in Trello a row will be added to a google drive spreadsheet. Use this with a recipe for tracking completed trello cards to be able to calculate how long each task takes.
Then
Add row to spreadsheet
This action will add a single row to the bottom of the first worksheet of a spreadsheet you specify. Note: a new spreadsheet is created after 2000 rows.
Explore more great ways to automate Google Sheets and Trello