Adding Limited Fields in Checkout Process

We require delivery instructions for many of our customers. However one of our couriers only allows 25 characters for this. The information is imported into our sage from our EKM website. One of our small team has to go through and amend the delivery instructions so they are only 25 characters which is very time consuming and on busy days can sometimes be missed. A field which can be limited to a certain amount of characters on the checkout screen would solve this issue.

My suggestion is that the admin of the website or EKM themselves should be able to add fields which can be limited to a set amount of characters on either the "Customer Details" screen or the "Order Summary" screen. For example a field which can only have 25 characters typed into it and will not allow anymore characters. I think that the limited fields would be a highly sought after addition to the site as many websites already implement similar limitations on data fields that customers have fill in information.