Part of Mexican life are the taco stands. There are very few during the day. There are some morning taco stands, like the Carnitas stand on Lazaro Cardenas and Aguacate that we frequent and is very popular with the Mexicans, but it is closed by 1:00 in the afternoon.
Another that I have been going to for years opens around 2:00 in the afternoon and is open until the evening. When I need something to eat in the afternoon and I am downtown, they are my go to place. Taco Gonzalez on Aguacate between Caranza and Lazaro Cardinas.
Most however don't open until around 7:00 or 8:00 in the evening after dark and there are taco stands on every street. That is my favorite time to go wandering around with a camera.

To me the lowly taco is the gourmet food of Mexico. For around 75 cents US, you can get a taco sincillo (plain) or with everything (beans, chopped onion, cilantro) and what distinguishes each taco stand are their salsas. They have to have at least 3, a red salsa, a green salsa, a guacamole salsa. They also serve quesadillas with the same options.
For meat, there is carne asada (grilled beef), adobada (pork marinated in a red dried chili adobo sauce) and al pastor (pork meat marinated and stacked on a vertical spike with a vertical grill). Meat is sliced off on the surface as it cooks with a little slice of pineapple. Also there is cabeza (meat from the head of the cow, not brains, just lips, cheeks, etc.) and Carnitas (which is pork meat cooked in a caldron of pork fat) but these are only served at breakfast. Each taco stand has its own specialties.
Another lunch taco is fish tacos. Here the favorite style is Baja style which is fish or shrimp dipped in batter and deep fried. They are served with shredded cabbage and usually mayonnaise or a chipotle mayonnaise plus the other usual salsas. They are usually a lunch thing. Our favorite is called Marisma on Naranjo and Caranza. They make their own corn tortillas heco a mano (made by hand) fresh hot and good.