Hi Maryann,
You can do a table service lunch and dinner in the same day on the dining plan. The plan is very flexible. You start out your vacation with a certain allotment of table service, counter service, and snack credits. As you use your credits, your receipts show you how many you have left. You start off with one credit each for each night of your stay. For example, if you are staying for 5 nights/6 days you get 5 table service credits.
If you find that you are having more than one table service meal per day, you may want to consider paying out of pocket for less expensive meals. Our family eats three meals a day most days on vacation. We will often pay for a buffet breakfast out of pocket or a less expensive quick lunch at a table service restaurant.
One thing that we like to do is eat lunch at a Signature Dining restaurant like the
Hollywood Brown Derby for lunch. For us, it doesn't seem worth it to use two table service credits, so we pay out of pocket. It really isn't too expensive for lunch, the food is delicious, and the atmosphere is wonderful.
Enjoy your trip and all the great restaurants of WDW