Day 22 covers all of Chapter 17, The Variety of Merits.

Having last month heard in gāthās of the innumerable merits to obtained by understanding by faith the longevity of the Buddha, we consider those who have firm faith.

Those who firmly believe [my longevity ],
And have no doubts about it
Even for a moment,
Will be able to obtain more merits [than he].

The Bodhisattvas who have practiced the Way
For the past innumerable kalpas,
Will believe my longevity
When they hear of it.

They will receive this sūtra on their heads,
And wish:
“May we live long and save all living beings
Just as the World-Honored One of today,
Who is the King of the Śākyas, [saves them]
By expounding the Dharma without fear
At the place of enlightenment
With [a voice like] a lion’s roar!
When we sit at the place of enlightenment,
Respected by all living beings,
May we preach that we also shall live
As long [as the World-Honored One of today]!”

Those who have firm faith,
And who are pure and upright,
And who hear much and memorize all teachings,
And who understand my words
According to their meaning,
Will have no doubts [about my longevity].

No doubts here.