From co.com:

Dining

48 U.S., Alaska, Canada, the Caribbean and Latin America Resort Destinations*
In general, meals or snacks are served in First Class on flights over 1 1/2 hours and in Economy Class on flights over two hours that fall within standard mealtimes. Beverages are served on all flights.

Standard Mealtimes
Breakfast / Snack: 7:00 a.m. - 9:00 a.m.
Lunch / Snack: 11:00 a.m. - 1:00 p.m.
Dinner / Snack: 5:00 p.m. - 7:00 p.m.

In addition, a light snack is offered in First Class as noted below:

Flights over two hours: 5:00 a.m. - 7:59 p.m.
Flights over three hours: 8:00 p.m. - 4:59 a.m.


The time is measured by the time zone of the originating city. So, the 1:12 departure from IAH never makes it into the 5:00 pm Central meal window as measured by city of origin. The 2:30 pm from LGA does make it into the 5:00 pm Eastern meal window, but barely, so they do not bother with a full meal.

What really is a travesty is when flights like CLE-SFO only get the snack because they are not considered true transcon and are outside the standard meal windows as measured by city of origin.