Mexican cuisine is primarily a fusion of indigenous Mesoamerican cooking with European, especially Spanish, elements added after the Spanish conquest of the Aztec Empire in the 16th century. The basic staples remain native foods such as corn, beans and chili peppers, but the Europeans introduced a large number of other foods, the most important of which were meat from domesticated animals (beef, pork, chicken, goat and sheep), dairy products (especially cheese) and various herbs and much spices.

While the Spanish initially tried to impose their own diet on the country, this was not possible and eventually the foods and cooking techniques began to be mixed, especially in colonial era convents. African and Asian influences were also introduced into the mixture during this era as a result of African slavery in New Spain and the Manila-Acapulco Galleons. Over the centuries, this resulted in various regional cuisines, based on local conditions such as those in Oaxaca, Veracruz and the Yucatán Peninsula. Mexican cuisine is closely tied to the culture, social structure and popular traditions of the country. The most important example of this connection is the use of mole for special occasions and holidays, particularly in the South and Center regions of the country. For this reason and others, Mexican cuisine was added by UNESCO to its list of the world’s "intangible cultural heritage".
(Wiki)

An average household would usually have 3 big meals a day, desayuno, comida y cena; breakfast being the heartiest one, takes place first thing in the morning, anytime between 7 -10 am. After that comes lunch, also quite heavy, anywhere from 2 to 5pm and dinner is commonly served around 7pm.

https://www.thecuriousmexican.com/breakfast-in-mexico/:
During lunchtime, we tend to indulge in a 4 course meal. We start with a warm soup, followed by the carb choice of rice or pasta, a main dish that could normally be a stew composed of meat and veggies like potatoes, and then followed by a sweet note with a small dessert. This is something you would normally eat at home or you could also find it by the name of comida corrida in small family-owned eateries called fondas.

Dinner, which at times might be called merienda, consists of a small meal or snack to help your body make it through the night. Some people believe that smaller nighttime meals is a healthier way to eat since your body doesn’t need much energy to sleep.

Of course, all the rules change completely over the weekends, as some people tend to wake up later and/or hungover (no judgement here, we’ve all been there) and usually just have one heavy meal for both breakfast and lunch, think of what you know as brunch, it’s just not called that in México, but if you say almuerzo, most people would understand what you’re talking about.