The Dining Plan credits are allocated per NIGHT of your stay at WDW. If you are spending six nights at a WDW resort and are on the basic Disney Dining Plan, you will be given six table service credits, six counter service credits and six snack credits. This is true even if you will be in the parks for seven days. (Follow the links I give in the postÂ
HERE for more details.)
You may use your credits in any order you wish. For example, you could use three of your table service credits on your first day and then none on the next two days. You could use all your table service credits for breakfasts and counter service for dinner. Really, whatever works for your style of vacationing.
While your credits are allocated by the number of nights of your stay, you can still use them up until midnight of the day you check out of your resort. So, this effectively means that you could be using credits on the 7th day of your trip, even if you were allocated only six days worth of credits, depending on how you chose to use them during the week. However, after midnight on your check-out day, any credits you have left will expire.
Hope this helps.