@Cassandra
All of my dogs are made to order, so I understand what you are going through. I state my dogs are made to order in my policy, shop announcement, and I send each customer message stating the process time. I still have customers tell me "need it by XX" after they place an order. I think it doesn't matter how many times you write it on your policy/shop announcement etc. There are always some people who don't read them. When I receive a note like "need it by XX" from a customer, I make sure to send them convos letting them know I need to upgrade shipping to Express mail etc. You will be surprised how many people are willing to pay for shipping upgrade and how many people can actually wait. I don't think I ever had any customers who canceled their orders because they didn't want to pay for shipping upgrade. They either payed or waited. Of course, you should say "no" if your customer is not willing to pay shipping upgrade or wait.
@BeaG
I understand what you mean but it is difficult when you receive many orders. Also, some items sell more than the other, and this month's best seller may not sell at all next month. Since your customers are willing to wait 5 to 12 days for the package to arrive, I'm sure they would wait for 1 week plus shipping (normally 2 to 5 days within the US, so still up to 12 day just like yours) for their order.