There is no time of the day that you can only eat salad. Often times, salads are eaten at lunch time around noon. The reason is because salads are usually light meals if they are eaten alone. They contain a lot of vegetables and a little meat, so they are not as filling as other meals. However, people want to eat lighter meals at lunchtime because they will have to go back to work.
However, some people eat salads at dinner time, but they are usually not eaten as one whole meal. Instead, they are eaten as a side dish along side an entrée. That is not to say, that salads can’t be eaten as a whole meal. Taco salads are often dinner meals.