The first line of this article from the Harvard Gazette says it all:

“Students with less than 20 minutes to eat school lunches consume significantly less of their entrées, milk, and vegetables than those who aren’t as rushed, according to a new study from the Harvard T.H. Chan School of Public Health.”

Those who say that there’s just no more time need to understand that not eating a proper lunch can have a large number of (unintended) negative consequences, including issues with learning and behavior problems.