If the conditions (eg: "ships in 4 - 6 days) are unique to each product, then this looks like it will involve the dbase - as you will have to insert those variables when uploading / editing a product's details.

So you would need to modify the php files that govern product data input, create an input field, modify or add a table in the dbase, and also consider how/where that data is output (in the browser, on confirmation e-mails, etc).

This is, I believe, a complete module in its own right, so you'd either have to code it yourself, or solicit some consultancy in appropriate places in the forum.