Most interesting. As a layperson I have trouble understanding what happens 17:00 to 06:00 the next day. What does it mean to "flag down" if you are still running 911 calls all night?
If you are at a busy station that typically is the time you get the snot kicked out of you. That is, every time you put your head down the "tones" go off and you get back into the truck to handle a problem for the citizens of your community. Some problems are real, some are perceived, and most just need a firefighter/EMS person to tell them what they should do.
Flag down was captured perfectly by @throwanem.
In this case I think "flag down" just means "no responsibilities other than responding to calls."
ETA: Indeed, 4 USC 6(a) [1]:
It is the universal custom to display the flag only from sunrise to sunset on buildings and on stationary flagstaffs in the open. However, when a patriotic effect is desired, the flag may be displayed 24 hours a day if properly illuminated during the hours of darkness.
To the best of my understanding, no criminal penalty attaches to mishandling a flag in contravention of Title 4 requirements, despite the occasional misguided attempt to prosecute someone who, for example, incinerates a symbol of his nation in order to attempt some sort of point about the present conduct of its government. That said, it would surprise me to learn that anyone who flies the flag for patriotic reasons would disregard a legal recommendation regarding the proper manner of such display.
The cited provision requires nothing, it is purely descriptive (“it is the universal custom that...” is not “everyone who flies a flag shall...”)
> To the best of my understanding, no criminal penalty attaches to mishandling a flag in contravention of Title 4 requirements,
There is, for actual requirements, like those regarding advertising use of the flag in 4 USC Sec. 3. But section 6 subsections either describe custom or describe what “should” be done, and thus are not requirements in any sense.