It is based on the number of nights you stay.
So that would be 5 TS meals, 5 QS meals, and 5 snacks per person on the regular dining plan (not quick service or deluxe plan - those are different). You can use them on your arrival day and up to midnight on your departure day. Couple of things I've learned over the years that I did not fully understand the first time we were on the dining plan
1) Credits are not tied specifically to an individual
2) Credits do not have to be used 1 per day
3) You do not all have to use your DP credits at a meal (except for buffets and price fixed / family style restaurants like O'Hana)
4) You can share meals on the DP (again not at buffets or price fixed places)
So what does this mean? It means that you can choose to share meals and/or pay out of pocket for some items so that you can do a Signature Meal or other package that requires 2 TS credits.
This last week we did all of the following:
1) At Sci Fi 2 of us ordered steaks, desserts, and drinks and used the DP while 2 of us ordered $9 salads and shakes and paid OOP.
2) At QS restaurants on several occasions DH and I shared a meal. We cashed in leftover QS credits for 3 snacks at both CSR and at the caramel place in Germany
3) At San Angel 2 of us ordered full meal with drinks and desserts and used DP while 2 of us just ordered an entree and water and paid OOP.
This was done so that we could do the Candlelight Processional which was 2 TS credits.