I used to work for a mail house. Our specialty was turning printed materials into mail. We didn't do the printing. Our customers would order materials from a printer, or sometimes several printers, and have them delivered directly to us. (Maybe envelopes would come from one printer, cover letters from another printer, brochures from still another printer, etc.) We would assemble them, add mailing addresses, apply postage (if necessary), and so on, and finally deliver the finished product to the Postal Service.
I found that the following rules applied:
1. If a customer tells you, "This job will be just like the last one you did for us," they will order materials unlike anything you have ever seen before.
2. If a customer tells you, "The materials will be delivered to you sometime this week," the materials will arrive either late Friday afternoon or early the following Monday.
3. Every Friday afternoon you will get several phone calls from printers asking, "How late are you open?"
4. If it is a rush job and you have scheduled people to work overtime on the weekend, the materials will arrive Monday. If you haven't, they will arrive Friday.
5. If the materials arrive on Friday, there will be something wrong with them which you won't notice until Monday.
6. If you call the customer on Monday, you will find that they are taking a few days off, "having just finished a big mailing project."