We can't let this happen again. We need to build a secure TWO-day-before-retirement safe room.
The comic plays with the TV and film trope of Retirony, in which a cop is killed in action only a short time before (often the day before) retirement, usually producing a sense of even greater tragedy in the timing of the death. The humor of this strip arises from the notion that, given so many policemen are killed the day before retirement, retiring cops could be sequestered in a secure facility on the day before their retirement to avoid retirony. Unfortunately this merely results in tragedy when a cop is killed the day before being sequestered.
The title text is a reference to the reactionary nature of security procedures often put in place in the aftermath of an incident, and how they typically fail to address the root cause of the problem. If the logic expressed in the title text was followed repeatedly, eventually the number of days police officers spent in the secure room would encompass their entire career. Perhaps even quicker, if combined with another expandable scheme designed to protect rookie cops from similar 'first day accidents'.
See also the paradox of the "unexpected hanging".