Question: Of Hans Pfitzner and Gaetano Donizetti, which composer's work was produced earlier? 

Context articles: Gaetano Rossi
Hans Pfitzner
Das Christ-Elflein
Gaetano Donizetti
Luise Willer
Die Rose vom Liebesgarten
Palestrina (opera)
Una follia
Il furioso all'isola di San Domingo
Eugenio Cavallini

Gaetano Rossi (18 May 1774 – 25 January 1855) was an Italian opera librettist for several of the well-known "bel canto"-era composers including Gioachino Rossini, Gaetano Donizetti, and Saverio Mercadante in Italy and Giacomo Meyerbeer in one of his early Italian successes.
 Other composers with whom he worked included Simon Mayr, a composer and Donizetti's teacher, as well as the prolific Giovanni Pacini.
Hans Erich Pfitzner (5 May 1869 – 22 May 1949) was a German composer and self-described anti-modernist.
 His best known work is the post-Romantic opera "Palestrina", loosely based on the life of the sixteenth-century composer Giovanni Pierluigi da Palestrina.
Das Christ-Elflein ("The Little Elf of Christ") is an opera in two acts by Hans Pfitzner to a German-language libretto by Pfitzner and Ilse von Stach.
 The work was originally premiered in 1906 as a Christmas play by von Stach with incidental music by Pfitzner.
 It was later revised by the composer into a two-act opera (the version performed today) which premiered in Dresden on 11 December 1917.
Domenico Gaetano Maria Donizetti (] ; 29 November 1797 – 8 April 1848) was an Italian composer.
 Along with Gioachino Rossini and Vincenzo Bellini, Donizetti was a leading composer of the "bel canto" opera style during the first half of the nineteenth century.
 Donizetti's close association with the bel canto style was undoubtedly an influence on other composers such as Giuseppe Verdi (1813–1901).
Luise Willer (1888–1970) was a German operatic contralto.
 She made her professional opera debut in 1910 as Annius in Wolfgang Amadeus Mozart's "La clemenza di Tito".
 She spent most of her career performing at the Bavarian State Opera in Munich.
 At the Bayreuth Festival, she portrayed Brängane in "Tristan und Isolde".
 She created roles in several world premieres during her career, including Barbara in Erich Wolfgang Korngold's "Violanta" (1916), Lukrezia in Hans Pfitzner's "Palestrina" (1917), Graben-Liese in Franz Schreker's "Das Spielwerk" (1920), and Herzogin in Pfitzner's "Das Herz" (1931) among others.
Die Rose vom Liebesgarten is a 1900 opera by Hans Pfitzner to a libretto by James Grun, one of Pfitzner's fellow students at the Frankfurt Conservatory, which had been prompted by an 1890 painting by Hans Thoma "Der Wächter vor dem Liebesgarten".
Palestrina is an opera by the German composer Hans Pfitzner, first performed in 1917.
 The composer referred to it as a "Musikalische Legende" (musical legend), and wrote the libretto himself, based on a legend about the Renaissance musician Giovanni Pierluigi da Palestrina, who saves the art of contrapuntal music (polyphony) for the Church in the sixteenth century, through his composition of the "Missa Papae Marcelli".
 The wider context is that of the European Reformation and the role of music in relation to it.
 The character of Cardinal Borromeo is depicted, and a General Congress of the Council of Trent is the centrepiece of Act II.
Una follia is an opera in one act by composer Gaetano Donizetti.
 The work premiered on 15 December 1818 at the Teatro San Luca in Venice.
 The opera uses the same Italian-language libretto by Bartolomeo Merelli after August von Kotzebue's "Der Graf von Burgund" that Donizetti used for his "Enrico di Borgogna" a month earlier, but with different music.
 It was given one performance and "never performed again, and its score has never been found."
Il furioso all'isola di San Domingo "(The Madman on the Island of San Domingo)" is a "romantic melodramma" in two acts by the composer Gaetano Donizetti.
 Jacopo Ferretti, who since 1821 had written five libretti for Donizetti and two for Rossini (including "La cenerentola"), had proposed the unusual subject and he was contracted to write the Italian libretto based on a five-act play of the same title by an unknown author in 1820, which "had been given in the same theatre [...] and which Donizetti had immediately loved".
 However, as has been noted by Charles Osborne, the "ultimate derivation of both play and libretto is an episode in part 1 of "Don Quixote" by Miguel de Cervantes's published in 1605" which is the story of Cardenio and Lucinda.
Eugenio Cavallini (16 June 1806 — 11 April 1881) was an Italian conductor, composer, violinist, and violist.
 In 1833 he became first violinist of the orchestra at La Scala, a post he held through 1855.
 He also served as a conductor at La Scala, notably leading the world premieres of Gaetano Donizetti's "Lucrezia Borgia" (1833), Donizetti's "Gemma di Vergy" (1834), Donizetti's "Maria Stuarda" (1835), Saverio Mercadante's "Il giuramento" (1837), Mercadante's "Il bravo" (1839), Giuseppe Verdi's "Oberto" (1839), Verdi's "Un giorno di regno" (1840), Donizetti's "Maria Padilla" (1841), Verdi's "Nabucco" (1842), Verdi's "I Lombardi alla prima crociata" (1843), Verdi's "Giovanna d'Arco" (1845), Federico Ricci's "Estella di Murcia" (1846), and Domenico Ronzani's "Salvator Rosa" (1854).