TL;DR — You aren’t likely to find something perfectly suitable through your approach to creating a compound word with both parts flipped. Folks normally use either in the dark or else by dark or by night to oppose in/by daylight. However, you might try moonshine.
The OED gives several examples of nightblack used to mean as dark as night, including these two:
- 1817 Shelley Rev. Islam i. lii, ― On nightblack columns poised.
- 1872 Tennyson Gareth & Lynette 1346 ― High on a nightblack horse, in nightblack arms.
It also attests the existence of night-dark, as in this citation:
- 1879 E. Arnold Lt. Asia 39 ― The night-dark steed.
What’s an Antonym?
I don’t think you will ever get a one-word opposite of daylight that fits perfectly in all places where daylight is used. Daylight a very old word dating from the thirteenth century which has come to be used in numerous ways:
- as a noun with any of several completely different meanings:
- the light of day
- the period between dawn and dusk
- the moment when the sun first clears the horizon, so dawn, daybreak, sunrise
- public awareness
- the space between two things
- as an attributive noun like daylight hours
- as an adjective like in daylighted buildings or daylighting techniques
- in opposition to the adjective standard in time zone names like Mountain Daylight Time opposed to Mountain Standard Time
- as a verb (both transitive and intransitive) for bringing something to the surface, like a buried creek or building
- in idiomatic expressions like to burn daylight and the living daylights
The top twenty collocations from COCA that immediately precede daylight are in order of occurrence
broad, during, before, eastern, into, see, until, full, bright,
still, local, saw, natural, pacific, enough, fading, central, seen,
open, and ambient.
The top twenty collocations from COCA that immediately follow daylight are in order of occurrence
hours, time, saving, savings, left, between, basement, came, film,
outside, raids, streams, faded, comes, fades, bombing, attack, raid,
revealed, and pours.
Your antonym presumably has to work in most of those places, and I don’t think you are going to come up with one. You appear to believe that one can derive a reversible antonym of a compound word by inverting each of its pieces and putting them back together again. That is not going to work in the general case, and it does not in general work here in this specific one either. These are almost none of them sensible:
- weekend: daystart
- today: fromnight
- tomorrow: yestereve
- everyday: nonight
- moonlight: sundark, stardark
- sunup: moondown, shadedown
- latterday: formerdark
- yuleday: lithenight
- day watchman: night listenwomen
- sunrise: moonset, shadefall, nightfall
- daylaborer: nightleisurer
- lifetime: deathspace
- daywork: nightplay
- firework: waterplay
As you see, most of those just don’t work at all. Sometimes you even find yourself back to the same place you started due to “double negation”, such as when you oppose sunup with shadedown — which would mean the same thing.
I’m not very fond of question that ask for neologisms, since that becomes nothing but a list question. However, because you limited it to actual published words, there is some small hope of rescuing your question.
Now, you have chosen to limit the sense of daylight to the first one I listed above, which also happens to be its oldest use: the light of day, the day’s light. That’s unfortunate because the only reasonable opposite for light of day is dark of night.
However, you do often find moonshine used as an opponent to daylight. For example:
He found he could hide from daylight and moonshine, and make his way swiftly and softly by dead of night with his pale cold eyes, and catch small frightened or unwary things.
―The Lord of the Rings, by JRR Tolkien
On the other hand, you have by night opposing by daylight here:
Though I could forget it by daylight, forcing it, so to speak, away from my consciousness with worries about the presence or absence of soldiers, and the thousand lovely images of peak and cataract and swooping valley that assailed my eyes on every side, it returned by night, when, huddled in my blanket and cloak and burning with fever, I believed I heard the soft padding of its feet, the scraping of its claws.
―Sword of the Lictor, by Gene Wolfe
Neither of those are new words; they’re just what people use, and so probably what you should use as well.
If you had elected the “sunrise” sense instead, there actually are neologisms coined by published authors for what the opposite of that would be. For example, Gene Wolfe uses shadelow and shadeup in his Book of the Short Sun and Book of the Long Sun portions of his Solar Cycle.
From shadeup to
shadelow, the sun had been a torrent of white fire across a dazzling
sky; the wind, fair and strong at morning, had veered and died away
to a breeze, to an occasional puff, and by the time the market
closed, to nothing.
―Caldé of the Long Sun, by Gene Wolfe
“You think I couldn’t? You think it because I’ve always been gentle with you for
your mother’s sake. It wasn’t like that in my family, believe me. Or in hers either. If you find yourself begging me before shadelow tomorrow,” to emphasize my point, I struck the table with the handle of the knife, “will you admit you were wrong? Are you man enough for that?”
―On Blue’s Waters, by Gene Wolfe
A round gold sun that walks across the sky during the course of the day, and vanishes into the sea at shadelow.
―Return to the Whorl, by Gene Wolfe
It’s too bad you have chosen the “light of day” sense of daylight, because Wolfe’s coinings are appealing for describing the dark and shady period between shadelow and shadeup.