“Better ten days of love than years of regretting.”

Original: Mieux vaut faire, et se repentir / Que se repentir, et rien faire
Source: Quatrains, LXXVIII

Attributed in "Duce (1922-42)" in TIME magazine (2 August 1943)
Also quoted by Generale Armando Diaz in "Il pensiero dei leoni" in Il Carroccio. The Italian review (1922) attributed to graffiti by an unknown soldier https://archive.org/stream/ilcarroccioitali15newyuoft#page/14/mode/2up
Though not precisely a repetition of any of them, this is somewhat resembles far earlier remarks attributed to others:
An army of sheep led by a lion is better than an army of lions led by a sheep.
Attributed to Alexander the Great, in The British Battle Fleet : Its Inception and Growth Throughout the Centuries to the Present Day (1915) by Frederick Thomas Jane
To live like a lion for a day is far better than to live like a jackal for a hundred years.
Tipu Sultan, as quoted in Encyclopedia of Asian History (1988) Vol. 4, p. 104
It is far better to live like a tiger for a day than to live like a jackal for a hundred years.
Tipu Sultan, as quoted in Tipu Sultan : A Study in Diplomacy and Confrontation (1982) by B. Sheikh Ali, p. 329
I should prefer an army of stags led by a lion, to an army of lions led by a stag.
Chabrias, as quoted in A Treatise on the Defence of Fortified Places (1814) by Lazare Carnot, p. 50
He has been frequently heard to say, that in this world he would rather live two days like a tiger, than two hundred years like a sheep.
Tipu Sultan, as quoted in A View of the Origin and Conduct of the War with Tippoo Sultaun; Comprising a Narrative of the Operations of the Army under the Command of Lieutenant-General George Harris, and of the Siege of Seringapatam (London, G. and W. Nicol, 1800) by Alexander Beatson, pp. 153-154. http://oudl.osmania.ac.in/bitstream/handle/OUDL/7905/212261_Origin_And_Conduct_Of_The_War_With_Tipoo_Sultaun.pdf https://indianhistorybooks3.files.wordpress.com/2014/06/99999990039373-view-of-the-origin-and-conduct-of-the-war-with-tipoo-sultan.pdf
1940s

Source: The Letters of Machiavelli

Gottfried to Jean-Christophe. Part 3: Ada
Jean-Christophe (1904 - 1912), Youth (1904)
Source: Jean Christophe Vol I
Context: Be reverent before the dawning day. Do not think of what will be in a year, or in ten years. Think of to-day. Leave your theories. All theories, you see, even those of virtue, are bad, foolish, mischievous. Do not abuse life. Live in to-day. Be reverent towards each day.
Context: Be reverent before the dawning day. Do not think of what will be in a year, or in ten years. Think of to-day. Leave your theories. All theories, you see, even those of virtue, are bad, foolish, mischievous. Do not abuse life. Live in to-day. Be reverent towards each day. Love it, respect it, do not sully it, do not hinder it from coming to flower. Love it even when it is gray and sad like to-day. Do not be anxious. See. It is winter now. Everything is asleep. The good earth will awake again. You have only to be good and patient like the earth. Be reverent. Wait. If you are good, all will go well. If you are not, if you are weak, if you do not succeed, well, you must be happy in that. No doubt it is the best you can do. So, then, why will? Why be angry because of what you cannot do? We all have to do what we can.... Als ich kann.

Source: The Real Frank Zappa Book

Babak Khorramdin's letter to his son, rejecting the caliph’s amnesty message, quoted by Al-Tabari, edited by C. E. Bosworth, History of al-Tabari Vol. 33, The: Storm and Stress along the Northern Frontiers of the 'Abbasid Caliphate: The Caliphate of al-Mu'tasim A.D. 833-842/A.H. 218-227 https://books.google.com/books?id=Ky2rl0xN2SQC&pg=PA74&lpg=PA74&dq=%22Better+to+live+for+just+a+single+day+as+a+ruler+than+to+live+for+forty+years+as+an+abject+slave.%22&source=bl&ots=D6-WGySNBR&sig=9MJm8qw6MeNgY1kPHEjtcxA_okY&hl=en&sa=X&ved=0CCoQ6AEwAmoVChMI2YO62Pb0xwIVjOwUCh2l8APi#v=onepage&q=%22Better%20to%20live%20for%20just%20a%20single%20day%20as%20a%20ruler%20than%20to%20live%20for%20forty%20years%20as%20an%20abject%20slave.%22&f=false

As quoted in Encyclopedia of Asian History (1988) Vol. 4, p. 104
Variants:
It is far better to live like a lion for a day than to live like a jackal for a hundred years.
It is far better to live like a tiger for a day than to live like a jackal for a hundred years.
Variant mentioned in Tipu Sultan : A Study in Diplomacy and Confrontation (1982) by B. Sheikh Ali, p. 329

Source: Babak Khorramdin's letter to his son, rejecting the caliph’s amnesty message, quoted by Al-Tabari, edited by C. E. Bosworth, History of al-Tabari Vol. 33, The: Storm and Stress along the Northern Frontiers of the 'Abbasid Caliphate: The Caliphate of al-Mu'tasim A.D. 833-842/A.H. 218-227 https://books.google.com/books?id=Ky2rl0xN2SQC&pg=PA74&lpg=PA74&dq=%22Better+to+live+for+just+a+single+day+as+a+ruler+than+to+live+for+forty+years+as+an+abject+slave.%22&source=bl&ots=D6-WGySNBR&sig=9MJm8qw6MeNgY1kPHEjtcxA_okY&hl=en&sa=X&ved=0CCoQ6AEwAmoVChMI2YO62Pb0xwIVjOwUCh2l8APi#v=onepage&q=%22Better%20to%20live%20for%20just%20a%20single%20day%20as%20a%20ruler%20than%20to%20live%20for%20forty%20years%20as%20an%20abject%20slave.%22&f=false