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Of British dialectal origin, the colloquial noun sparrowfart, and its variants, designate the break of day.

With humorous allusion to a small passerine breaking wind (cf. “afore th’ sparrow farts” in quotation 1.3 below), the noun sparrowfart refers to the dawn chorus—i.e., to the early-morning bird song.

The noun sparrowfart occurs, for example, in an article about the BBC television programme Countryfile, which reports on rural, agricultural and environmental issues—article by Fiona Sturges, published in The Guardian (London and Manchester, England) of Saturday 28^th July 2018 [page 37, column 1]:

Gnarly hellraiser Iggy Pop is a big fan, which is actually quite fitting given his resemblance to a 200-year-old yew tree. Royal numpties Charles and Camilla also love it, which has led to some right royal bum-licking—barely a month seems to go by without the heir to the throne being given carte blanche on the show to bang on about his latest agricultural passion with the enthusiasm of a mega-rich landowner who will never be required to get up at sparrow-fart to shovel shit.

These are, in chronological order, the earliest occurrences of the noun sparrowfart and variants that I have found:

1.1-: From The Dialect of Craven, in the West-Riding of the Country of York, with a copious Glossary (London: Printed for William Crofts, 1828), by William Carr (died 1843) [second edition, volume 2, page 152]—A. S. stands for Anglo-Saxon:
—Note: It is interesting that (probably because fart was then regarded as coarse slang) William Carr felt the need to invent a ‘learned’ erroneous etymology:

SPARROW-FART, Break of day, very early. It is said to be three hours before day-light. This truly ludicrous expression is, I think, a corruption of sparkle-fert. A. S. speark, scintilla, et fert, crepitus, break of day.

1.2-: From A Glossary of Words used in the County of Chester (London: Published by the English Dialect Society, 1886), by Robert Holland (1829-1893) [page 331]:

SPARROWFARTS, s. very early morning.
“Tha mun be up by sparrowfarts or tha’ll be too late.”

1.3-: From The Folk-Speech of South Lancashire: A Glossary of words which are, or have been during the last hundred years, in common use in that portion of the County Palatine situated between Bolton and Manchester (Manchester: John Heywood, 1901), by Francis Edward Taylor [page ?]:

SPARROW-FART. A jocular term applied to the very early hours of the morning. “Aw’st ger-up afore th’ sparrow farts,” or “afore sparrow-fart.”

1.4-: From Rossendale Dialect Dictionary, compiled by George Nightingale, published in The Ramsbottom Observer (Ramsbottom, Lancashire, England) of Friday 9^th November 1917 [page 8, column 1]—Rossendale is in Lancashire:

Sparrowfart: A tterm [sic] applied to those individuals who rose very early in the morning; inquisitiveness.

The noun sparrowfart has come to be also—but rarely—used in the sense of an insignificant person or thing. These are three occurrences of that use:

2.1-: From Ulysses (Paris: Shakespeare and Company, 1922), by the Irish author James Joyce (1882-1941) [III, chapter 18: Penelope, page 713]:

Kathleen Kearney and her lot of squealers Miss This Miss That Miss Theother lot of sparrowfarts skitting around talking about politics they know as much about as my backside anything in the world to make themselves someway interesting.

2.2-: From I just called to say I loathe you, by the Scottish journalist and politician Dorothy-Grace Elder, published in Scotland on Sunday (Edinburgh, Midlothian, Scotland) of Sunday 7^th November 1993 [page 17, column 1]—BT stands for British Telecom:

For synchronised smarming, no one can beat BT. They have the best thought doctors in snowbusiness [sic]. They made us feel humbly grateful by knocking £130m off weekend calls—until, two days later, we discovered this was mere sparrowfart when they announced their latest profits… £1.6bn in six months.

2.3-: From No sympathy for the bonk of England, by the Scottish journalist and politician Dorothy-Grace Elder, published in Scotland on Sunday (Edinburgh, Midlothian, Scotland) of Sunday 26^th March 1995 [page 19, column 2]:

There was Rupert Bare, the arrogant cad with mandatory curling lip, brought to ruin; his careerist mistress scrunched into a ball of spitting cat fur; his society wife ruffling her bustle to do the old clinging vine standby routine. (Some women must fear work in the real world more than death). The whole business brought out the worst in us all—most enjoyably. Come on now, admit it: it was vintage schadenfreude to see three of the Knightsbridge over-privileged, all with those bad smell under the hooters expressions, scrapping like Kilkenny cats—pure dead common brilliant.
Not one of the trio deserves a sparrowfart of sympathy.