Can I add a field to the website front-end that an end-user enters data into, which gets saved to a backend field? (e.g., "x_studio_my_custom_field")

For context, I'm trying to add a "Delivery Date" field to quotes during the checkout process, for when the user wants a delayed product delivery. (Our products can be large and heavy, so timing the shipment to a day the customer can accommodate it is important)

I currently only have access to the Odoo web console (for custom XML/Javascript), but not the Odoo Python code/database.