Answer

Yes, in Jain cosmology, Kevalajñāna is not possible during:

• The last two aras of the present Avasarpiṇī
• The first two aras of the coming Utsarpiṇī

This period is traditionally understood as a spiritually declining and then very early spiritually undeveloped time, in which conditions are not suitable for attaining Kevalajñāna.

Explanation

In Jain Dharma, time moves in two great half-cycles:

• Avasarpiṇī — descending half-cycle
• Utsarpiṇī — ascending half-cycle

Each half-cycle has six aras.

We are currently in the 5th ara of Avasarpiṇī, called Duṣamā. After this, the 6th ara will come.

Traditionally, Kevalajñāna is possible only in suitable spiritual conditions. It is not possible in the extremely painful and spiritually unfavorable periods such as:

• 5th ara of Avasarpiṇī
• 6th ara of Avasarpiṇī
• 1st ara of Utsarpiṇī
• 2nd ara of Utsarpiṇī

The combined duration commonly associated with these four aras is:

• 21,000 years — 5th ara of Avasarpiṇī
• 21,000 years — 6th ara of Avasarpiṇī
• 21,000 years — 1st ara of Utsarpiṇī
• 21,000 years — 2nd ara of Utsarpiṇī

So:

21,000 × 4 = 84,000 years

That is why it is said that for 84,000 years, Kevalajñāna will not occur in this region of the time-cycle.

Important Clarification

The 84,000 years refers to the combined period of:

• remaining 5th ara of Avasarpiṇī,
• 6th ara of Avasarpiṇī,
• 1st ara of Utsarpiṇī,
• 2nd ara of Utsarpiṇī.

However, strictly speaking, since we are already inside the 5th ara, the actual remaining time from today is less than the full 84,000 years.

Takeaway

Your understanding is broadly correct: Kevalajñāna is not possible in the last two aras of Avasarpiṇī and the first two aras of Utsarpiṇī, and the traditional total duration of these four aras is 84,000 years.