Day 14 covers all of Chapter 9, The Assurance of Future Buddhahood of the Śrāvakas Who Have Something More to Learn and the Śrāvakas Who Have Nothing More to Learn, and opens Chapter 10, The Teacher of the Dharma.

Having last month considered Ānanda’s reaction to the prediction of his future Buddhahood, we hear Śākyamuni’s prediction for Rāhula.

Thereupon the Buddha said to Rāhula:

“In your future life you will become a Buddha called Walking-On-Flowers-Of-SevenTreasures, the Tathāgata, the Deserver of Offerings, the Perfectly Enlightened One, the Man of Wisdom and Practice, the Well-Gone, the Knower of the World, the Unsurpassed Man, the Controller of Men, the Teacher of Gods and Men, the Buddha, the World-Honored One. [Before you become that Buddha,] you will make offerings to as many Buddhas, as many Tathāgatas, as the particles of dust of ten worlds. [Before you become that Buddha,] you will become the eldest son of those Buddhas just as you are now mine.

“The adornments of the world of Walking-On-Flowers-Of­Seven-Treasures Buddha, the number of the kalpas for which that Buddha will live, the number of his disciples, the duration of the preservation of his right teachings, and the duration of the preservation of the counterfeit of his right teachings will be the same as in the case of Mountain-Sea-Wisdom-Supernatural-Power­King Tathāgata.

“After you become the eldest son of the [Mountain-Sea-Wisdom-Supernatural-Power-King] Buddha, you will attain Anuttara-samyak-saṃbodhi [, and become Walking-On-Flowers-Of-Seven­Treasures Buddha].”

Nichiren offers this explanation for the length of time needed for Rāhula to become a Buddha:

The śrāvaka disciples such as Ānanda, and Rāhula, who were guaranteed to be future Buddhas in the theoretical section of the Lotus Sūtra through the three cycles of the Buddha’s preaching (dharma, parable, and past relationships) had learned the Lotus Sūtra far in the past, 3,000 dust-particle kalpa (aeons) ago, from a bodhisattva who was the 16th prince of the Great Universal Wisdom Buddha, namely Śākyamuni Buddha today. Nevertheless, due to evil karma they abandoned the Lotus Sūtra, embracing such Mahayana sutras as the Flower Garland Sūtra, Wisdom Sūtra, Sūtra of Great Assembly, Nirvana Sūtra, Great Sun Buddha Sūtra, Revealing the Profound and Secret Sūtra, and Sūtra of Meditation on the Buddha of Infinite Life or Hinayana Āgama sutras. While doing so, they gradually declined in status to the realms of heavenly and human beings and finally to the three evil realms. As a result for as long as 3,000 dust-particle kalpa they spent much of their time in the Hell of Incessant Suffering, some of their time in the seven major hells, once in a long while in the other one hundred or so hells, and on rare occasions in the realms of hungry souls, beasts, and asura. It was after the 3,000 dust-particle kalpa (aeons) that they were able to be born in the realm of human or heavenly beings.

Kyōdai-shō, Letter to the Ikegami Brothers, Writings of Nichiren Shōnin, Volume 6, Followers I, Page 73