How many days do you usually plan your diet meals?

I usually have a light breakfast of two boiled eggs, an apple, Greek yogurt, and nuts.

For lunch, I eat a regular meal, choosing whatever I want and just adjusting the portion size.

And because I eat a light dinner consisting of things like fruit and sweet potatoes.

Aside from the daily changing lunch menu, I don't plan a separate diet.

I'm wondering if I should plan my lunch as well and eat more systematically.

I am also wondering how many days would be a good unit of time when creating a meal plan.