Hi Sandra,
  My family love the Disney Dining Plan and as you will be visiting the Walt Disney World Resort for 14-nights, you're going to be able to experience so many wonderful dining locations. 
 You will be able to start using your Disney Dining Plan meal entitlements as soon as you check-in at your Disney Resort hotel. You can redeem as many Quick-Service, Table-Service and Snack entitlements as you like each day of your stay until your total number of meal/snack entitlements has been depleted. 
 Any unused meals and snacks expire at midnight on your package reservation check-out date. 
 So in summary, you can start using your meal entitlements as soon as you have checked-in at your hotel on 18th August 2016 and can continue to use them until midnight on 1st September 2016 unless you have used them all up prior to then. 
 I would recommend that you take a look at the 
2016 Disney Dining Plan brochure as this contains lots of useful information about the Disney Dining Plan. 
 Wishing you a magical holiday filled with memories which will last a lifetime! 
 Emma