If the lead had an "Expected Closing" date (deadline), report how many days past this date the lead was eventually closed.

"How well are Salespeople meeting their close deadlines (if any)?"

How can you discover this answer yourself?

1. Review the Field (Fields Menu in Developer Mode):

2. Open the Python files in the models folder of the module (this one is defined in crm_lead.py - we normally name the files are the model they apply to).

3. Look for the field definition:

days_exceeding_closing = fields.Float('Exceeded Closing Days', compute='_compute_days_exceeding_closing', store=True)

In this case there is a compute method which defines the value, so you can review that code in the same file.