Technically, you can "submit a public comment" about these jokers anytime you want, and you should, but (as TSA News has been pointing out for a while), today is yesterday was the last day to submit one officially as part of the administrative notice-and-comment rulemaking process.
If you aren't familiar with that process, it takes place because a federal agency is required to give the public an opportunity to weigh in on proposed rules before putting those rules in place.
Or, if the agency is the TSA, it ignores that requirement and does what it wants to until a federal court "suggests" it should comply with the law, and then it ignores that "suggestion" for a year until the court specifically orders it to comply, and then it ignores the order for another year before finally offering travelers the chance to comment on rules that it put in place long ago.
That is, as you can see from the notice of proposed rulemaking, the TSA is "proposing to revise its ... regulations to clarify that TSA may use advanced imaging technology (AIT) to screen individuals at security screening checkpoints." By "advanced imaging technology" it means the scanners that irradiate you and let its agents see you naked. So, isn't that nice? It's planning to "clarify" that it "may" do something it's been doing for years and it's only doing that because a court ordered it to three years ago.
While Congress has ordered the TSA to get rid of the most invasive sort of scanners, the other kind is still in place (although that kind can also be easily fooled), along with useless patdowns and the billion-dollar SPOT behavior-detection program that DHS's own inspector general recently found does not work. Well, it doesn't work in terms of catching terrorists, but as 30 TSA agents in Boston reportedly told the ACLU last year, it did a decent job of hassling "African-American men wearing backwards baseball hats."
So, really, what's to complain about?
The real question, I suppose, is whether you should bother offering a comment at this point. [Not formally, because the comment period has closed.] I think you should, [or at least I did yesterday,] because even though the TSA doesn't much care what you think, there are some in Congress who do, at least to some extent. Also, a large number of comments reduces the TSA's ability to claim that people must be happy with what it's doing because few people bothered to complain. Silence is not assent, just like lots of people are not happy being scanned but put up with it because they have to catch a flight or whatever. That doesn't justify the practice. But non-silence is better.
Also, this takes very little time to do. Your comment doesn't have to be long or detailed, and you don't even have to type in a bunch of contact information. In fact, you don't have to type any, because you can submit comments anonymously (though somebody at the NSA is putting air quotes around "anonymously" right now). Nor does it even have to be about the scanners themselves. Feel free to use any of the above or any of the other griping in my "Homeland Insecurity" category, or maybe part of the Cato Institute's comments, linked here. Or take a look at some of the other comments people have already submitted.
They are overwhelmingly negative, but if you hunt for a while you can find a couple of positive ones if you need an example of that. It could happen.
Update: The comment period closed at midnight on Monday (when I originally posted this). Apologies for any wasted clicks this morning.