The theatrical phrase it will be (or it will come) all right at night (or all right on the night) means the opening night will go well.
These are the earliest occurrences that I have found, in chronological order:
1-: From Ellistoniana. No. VII. Playing to the Boxes, by the English playwright William Thomas Moncrieff (1794-1857), published in The New Monthly Magazine and Humorist (London: Henry Colburn) of July 1843—Robert William Elliston (1774-1831) was an English actor and theatre manager:
In the full tide and zenith of Elliston’s popularity during his first engagement at Drury Lane theatre, he one morning received an offer from a country manager, till then unknown to him, to star it for a few nights at a theatre in a somewhat remote part, on highly liberal sharing terms. The close of Drury Lane for the summer season, giving our great actor a congé for a few months, he resolved to embrace the offer […].
The rehearsal commenced—the royalty of Denmark, consisting of the King and Queen, with the chamberlain, old Polonius, were duly present; there was, however, no court. Elliston remarked this to the manager.
“I shall cloak the court, sir,” said the manager, “always cloak the supers here.” *
Elliston took this assurance in its literal sense, it being a theatrical technicality with which he was not then acquainted, and was satisfied.
“I hope too,” continued he, “this is not intended to be the scene—this cottage interior does not at all look like the royal halls of Elsinore.”
“It shall be all right at night, sir,” rejoined the manager.
In the subsequent platform-scene, Mr. Truncheon begged to stand up for the Ghost.
“Where is the gentleman who is to play the Ghost?” inquired Elliston. “Why does he not attend the rehearsal?”
“It shall be all right—the Ghost shall walk at night, sir, depend on it,” said the manager.
As the rehearsal proceeded, the prompter was obliged to read for Guildenstern and the Second Player.
“How is this?” inquired Elliston, waxing wrath.
“The Second Player will be doubled at night, sir,” said the manager,” and Guildenstern will be all right.”
“Really your company are very remiss in their attendance this morning,” said Elliston: “I fear you are not strict enough.”
“It will be all right at night, sir, be assured,” again reiterated the manager.
It now came to the last scene; the manager, who again stood up for Osric, apologised for the absence of the foils, as they had not arrived from the tinman, but pledged his word, they would be all right at night.
Elliston therefore went very amiably through the fencing-scene with the gentleman who was to play Laertes, both of them making the passes, thrusting, parrying, carte and tierce, with their hands.
The rehearsal now ended, and with the exception of the singing being left out by particular desire of the manager’s wife, who was to play Ophelia, and who only hummed the tunes, every thing really promised, as Mr. Truncheon had said, to be all right at night.
The play proceeded; but what was our actor’s astonishment, when, on being addressed by the usurping Claudius, he turned round and found, though assured it would be “all right at night,” that the majesty of Denmark was assembled in the identical rustic cottage he had reprobated so strongly in the morning, and that the whole court of Elsinore was comprised in the person of Mr. Truncheon, who was spreading himself out in a very suspicious cloak and beaver.
For a long time after this, Elliston was very particular in ascertaining the state of the premises when he went starring it in the country, and never again took it on credit that it would be “all right at night,” whenever he had any serious intention of “playing to the boxes.”
* To cloak a part is where the manager, prompter, or other official person goes on enveloped in a large cloak, for any unimportant part, for which there may happen to be no representative. An ingenious country manager has been known to go on, in a heavy play, for half the dramatis personæ by this curious expedient.
2-: From My Christmas Piece, and unsigned story published in the 1862 Christmas Number of London Society. An Illustrated Magazine of Light and Amusing Literature for the Hours of Relaxation (London: Printed by William Clowes and Sons)—the author recounts all the difficulties he had in mounting at the Theatre Royal the Christmas burlesque that he had written:
Looming in the immediate future, I see two other tormentors bearing down upon me with stolid and inexorable looks. Who is this frowsy, Polyphemus-looking man, who emerges from a cobwebbed cave under the stage to beckon me to a conference? He whispers of ‘properties.’ What can an author have to do with property, and in the plural too? Properties forsooth! ‘Will you come and look at your properties?’ My properties! Yes, I must go and look; I must waste a day taking stock of them, and seeing that they are in good condition. They consist probably of a crown and sceptre, a jewelled cup, a bugle, a sack, a club, a polished shield, a pig, a bottle of poison, a dagger, a bowl, a ball of worsted, a penny whistle. Were not all these articles carefully written down, as in an inventory, for the direction and guidance of Polyphemus? And yet he has forgotten the penny whistle and the sack, upon which so much depends . And the shield which is to be borne by the delicate and fragile Miss B. weighs half a hundredweight, and is not polished. The bowl, my friend, is to drink poison out of—not to wash in—I don’t want a basin; and as Miss A. has to carry the sack over her pink velvet doublet I think she will prefer one that has not recently contained a hundred of coals.
‘Oh, it will be all right at night.’
‘I think I have heard that remark before, my friend, and I think I have found the assurance not borne out by the event.’
3-: From The Miseries of a Dramatic Author, an unsigned essay published in The Cornhill Magazine (London: Smith, Elder and Co.) of October 1863:
It is unnecessary to say that not all actors are very intelligent and very complying. Even when intelligent, they are human beings, subject to the mutable motives and caprices of men. They have their interests to attend to, and their vanity to misguide them. Rehearsal brings these out. First let me note that it is only good actors who ever act at rehearsal; the others gabble over the words, and when by emphasis or manner they unmistakeably betray some misapprehension of the part, they answer your objections with the one invariable formula: “It will be all right at night.” You have horrible misgivings that it will be all wrong at night; but what can you do? Bad actors are unteachable, incorrigible. They will take no hint; they resent advice. […]
[Before] the First Night […] the dramatist […] has horrible misgivings. The last rehearsal was anything but perfect. Some of the actors had not yet mastered “the words.” It is to be all right at night; and he hopes it will be.
4-: From All the Year Round. A Weekly Journal. Conducted by Charles Dickens (London: Published by Messrs. Chapman and Hall) of Saturday 2nd December 1865:
WITH THE LORD MAYOR ON HIS OWN DAY.
I spent a whole day lately with the Lord Mayor of London, and the day I spent with him was his own day—the ninth of November. […]
Theatrical parlance is not inappropriate here, for the preparations going forward at the Guildhall at ten o’clock are strongly suggestive of the last rehearsal (with scenery and properties) previous to the production of the grand spectacle. A crowd of workmen are busy in the outer hall and corridors, laying down matting and carpets, hanging up flags and festoons, arranging guns and cutlasses in fancy devices over the doors, setting out pots of flowers and boxes of shrubs, nailing, sawing, planing, and hammering, showing the greatest activity, but yet giving little assurance that “it will be all right at night.”
5-: From the Birmingham Daily Mail (Birmingham, Warwickshire, England) of Thursday 22nd June 1871:
OF AMATEUR THEATRICALS.
By “The Odd Man Out.”
Many amateurs find rehearsals very trying; the cold, desolate theatre is cheerless and dispiriting; an uneasy feeling prevails that the actresses are laughing in their sleeves, and the “slop” jacketed scene-shifters disposed to chaff. The rehearsal seems so lax and slovenly that you can hardly place faith in the statement vouchsafed by the stage-manager that “it will be all right at night.” You leave with a despairing feeling that an awful failure is impending; but somehow things do come pretty right at night, and you get through usually without any more serious mishap than a few “waits” and a too liberal allowance of prompting.
6-: From the review of Fra Diavolo, an opéra comique by the French composer Daniel Auber (1782-1871), produced at Crystal Palace, London—review published in The Observer (London, England) of Sunday 8th September 1872:
The opera was creditably performed, but was certainly not very successful, owing apparently to the want of adequate rehearsals. Instead of that precision and “go” which are the result of careful stage rehearsals, there was an indecision, hesitation, and occasional blundering, which took away from the dramatic illusion. […] These inconsistencies are of no serious importance, but they are sufficient to destroy the desired illusion, and they might be avoided if sufficient rehearsals were secured. It is unfortunately the bane of English operatic schemes that sufficient attention is not paid to this point. Two or three rehearsals are generally thought quite sufficient for ordinary operas; and in the case of well-known operas like the “Bohemian Girl” or “Maritana” rehearsals are often dispensed with altogether. Frequently at an English rehearsal defects are visible which indicate the necessity of further study and rehearsal. But there is a comforting shibboleth which is invariably resorted to on such occasions. “It will be all right on the night,” says some one—every bystander takes the same optimistic view; and if the performance is not “all right,” but “all wrong,” on the night of performance, everybody concerned is certain that some one else is to blame.