Tolkien's final First Age timeline

[James the Just]

Happy New Year!

From Tolkien Gateway:

Unlike other reckonings of time created by J.R.R. Tolkien to set his legendarium, the Valian Years did not have a complete and definitive form. In the 1930s and 1940s, Tolkien handled a length of the Valian year fluctuated slightly around a round number of 10 solar years. In the notes to The Annals of Aman, Tolkien stated a single Valian year lasts 1,000 Valian days, defined as the duration of a complete flowering of the Two Trees of Valinor. Each of these Valian days is divided into 12 Valian hours, with each Valian hour having a duration equivalent to 7 solar hours. Thus, a single Valian year would last 84,000 solar hours. As a single solar year is approximately 8,766 hours, it was easy to calculate the equivalence of 9.582 solar years for each Valian year.

This is a little bit incorrect. According to Tolkien himself a year is 365 days, 5 hours, 48 minutes, and 46 seconds. This would be 8,765.812778 hours, for a Valian Year of 9.58268242 years.

But why did Tolkien choose a Valian Year of 84,000 hours to begin with? It seems rather odd. Perhaps there is an explanation.

The length of time from the new tally of years beginning with the Years of the Trees to the Years of the Sun is 1,500 Valian Years, or 14,374 mortal ones. This comes out to 99.82 Valian Years of the longer sort (144 years). What if he had an age of 100 Valian Years in mind? It seems too close to be coincidental. If that's the case then the short Valian Year would be exactly 9.6 years, not 9.582.