BigCommerce OnePage Optimized Checkout - Select Delivery Date + Order Comments

I’m trying to pass delivery details (selected by the customer on the cart page) into the Order Comments field at checkout by saving the data in

localStorage, then injecting it into the order comment input during checkout.

However, this isn't working. On the Checkout page, it seems my script does not execute. The "Preferred Delivery Date" and "Select Time Slot" info is not in the Order Comments Field. How can I make that work...? Help...

Our internal solution is to create a Select Delivery Data/Time input field above the comment box; have a user select it, then populate the comment field with a string. This is somewhat tricky, but it prevents another subscription fee.