I'd like to add a column that calculates time worked based on 2 time

I'd like to add a column that calculates time worked based on 2 time columns (start and end). It would be great if you could add a field for someone to add a custom calculation.

Not possible with the configurable list widget but that's doable using two date fields and perform the calculation.

Guide: http://www.jotform.com/help/259-How-to-perform-calculation-in-the-form

You might want to try this widget too https://widgets.jotform.com/widget/dates_difference.