You don't get credits per day at all. You get credits per night.
You are staying 7 nights, so on the basic plan each member of your party (age 3 or over) will recieve 7 TS credits, 7 CS credits, and 7 snack credits. You will receive all the credits at the same time when you check in on the 18th. You then have until midnight on the 25th to use all of them up. It doesn't matter what day you use them and how many of each type of credit you use on any given day.
For this reason it's suggested that if you are on the DDP you should plan your meals - decide ahead of time where you want to eat, on which day, and how many credits it will cost you.
You might want to see the "Everything you wanted to know about the dining plan" sticky thread at the top of this board.